I use a Steinberg UR22 MkII USB interface. It comes with ASIO drivers that can be configured to give very low latency.
A quality audio interface seems to be key to getting latency down into low figures, that and removing Windows processes that are unecessary.
There are various web sites that deal with tweaking Windows for performance.

When sequencing or working on audio, I make sure that Wi-Fi, Bluetooth and Ethernet connections are all deactivated, and that seems to ensure no glitches.
The PC is a fairly old Lenovo Thinkpad T430 running Windows 7 Pro. It's been tweaked with an SSD boot/program drive and a regular HDD.
Then there's an eSATA SSD with a few sample libraries on it.

I'm not trying to do anything really clever with it though, nor typically do I try creating hundreds of tracks.
I think the maximum was about 70 or 80 tracks on a really complex orchestral MIDI file.

Thanks ever so much, JohnG. This is the jackpot of golden Double Eagles I've been looking for on other subjects. The Roland UM-1 is the only good interface I've been aware of heretofore and it performs perfectly. Any idea how it compares with the Steinberg? I see a "Roland UM-One mk2" is marketed now.

AVG TuneUp always tells me too much is running in the background on my laptop, but I look up the programs it tells me to close and they all sound quite essential.

Gracious, you do up 70- or 80- piece orchestras! Seems to indicate more wonderful news. And oh the good it does me to read that you too use an older Windows 7 puter. At your suggestion am reading up on how to optimize it. Of course I use CCleaner, its equal or better lost twin Diskmax, and AVG TuneUp -- they make a HUGE difference. Boot up and down is vastly faster since I got the AVG. How can I ever thank you -- here, have a piece of music (unrelated to me):

https://www.youtube.com/watch?v=xkwx9CFdLQ0

You could use the Garritan Harps to (attempt) to realise the impromtu you posted. Nice and challenging!

No, I haven't compared interfaces between Steinberg and Roland.
I chose the UR22 Mk II because I have had quite good experiences with Yamaha equipment since about the mid nineties.
My feeling is that it is, most often, made up to a standard rather than down to a price, but with a close eye on the market place.

My first exposure was to an add on board for the old SoundBlaster cards, a DB50-XG. I was very impressed at the time.
That led to the list I quoted above as well as a Yamaha organ, an AN1x synth and a VL71m sound module for my Akai EWI4000.
All good bits of equipment, and well made.
Yamaha bought Steinberg back in the late nineties, as I recall, and I believe had a hand in building the UR22.
It had good reviews, so I went for that one.

Up to 70 or 80 tracks, as I recall, although by far the most usual is two to three dozen.

Glad some of what I posted helped.
I also have a web forum, now largely defunct, called MIDI-tutor.
There's some stuff there that you may find useful.

JohnG.

All keenly interesting -- further heartfelt thanks. Got a URL on your tutorial site? Tried googling it. Garritan's harps have the same problem as my Privias do -- they sound phenomenal in lower and middle range only. I wonder if Native Instruments or some other soundbank has better harps. The one on our Rodgers organ is stellar -- I use it all the time, and not only in organ range

I see your UR22 is a little box. Are they better the cord types?
https://www.roland.com/us/products/um-one/

How likely is it that my laptop, Sonar 7 (a program now at least 14 years old) and the Garritan Personal (or Pocket) Orchestra will suffice for my projects? My orchestral needs are extremely simple -- reasonably realistic piano/harpsichord/harp/celesta et al and solo and ensemble winds, strings, brass.

Glad you found it useful.

I'm sort of surprised you don't find the quality of the Garritan harps to your liking.
Gary Garritan is a harpist and as far as I'm aware did his utmost to make the library as realistic as possible.
Not being a harp enthusiast myself, I'm unable to give you further advice on suitable libraries.

I use the UR22 primarily as an audio interface.
My keyboard connects directly to the PC via it's own USB cable (so I don't need a USB/MIDI convertor).
It's a MIDI controller keyboard only, so it has no inbuilt sounds.
I.e. the MIDI key strokes enter the PC via USB, and are recorded in the sequencer, which has the Garritan ARIA player VST running in it,
which means I can hear the sounds as I play them.
I can then tweak my faulty playing to my satisfaction in the sequencer.

midi-tutor.proboards.com will get you there.

It's difficult for me to advise, from a distance, whether one laptop or another will suffice.
However, to do something like this in a relatively simple way, providing you're not expecting absolute marvels of production, is possible with a relatively modest computer.
An i5 Core 2 duo, with 8GB of memory should suffice to make a beginning.
Almost every PC does need to be tweaked to make it run efficiently though.
But, inevitably, as your expectations of sound quality increase and the more sample libraries you use grows, etc. the more powerful a machine will be needed.

MIDI sequencing has been going on since the days of the Atari home computers, and for sequencing only they didn't do a bad job.
It's only running virtual instruments at the same time as sequencing that requires significantly more computing power, memory and hard disk space.
I could actually do all of this on a laptop such I've described above, using a Yamaha program called SOL2 which dates back to around 2003.

JohnG.

Do you use those harps? Maybe they have a great full range in person. Maybe they're better since I looked into it a few years ago.

You've just described my exact computer (i5 dual core 8gb) so maybe there's hope. Based on pages like this
https://www.poweradmin.com/blog/how-to-optimize-and-speed-up-windows-7-performance/
.....I'd love to think CCleaner (the page recommends it) and DiskMax are optimizing my SSD enough. But do you think these categories are needed for my MIDI purposes:

#2. Disable unnecessary visual effects
#3. Update Windows with the latest definitions
#5. Disable unused Windows Services (??)
#11. Disable UAC (***Advanced Users Only!)
#12. Increasing the page file and allocating memory for Background services

Re, #3, the latest definitions of what? I haven't updated Windows in the 4-5 years since MS tried to force Win10 on everybody via that route. It has caused no problems I'm aware of.

To be honest, although I did buy the harps some time back, I've never had the need to use a harp as a solo instrument, so I tend to use, when needed within an orchestra, the much simpler harp included in the GPO5 library. I'm no expert here.

One of the reasons I choose to use this library is because the sample playback uses a mechanism to define its parameters called "sfz".
This description is in the public domain and it means that the text files can be edited to change playback if so desired or if the occasional 'bug' is found.

In terms of optimisation I didn't have to do much just for MIDI, it was only when I started to use virtual instruments that performance needed tweaking.
I seem to recall that optimising for background services is one of the recommendations for MIDI, I'm not quite so sure when it comes to MIDI and audio.

I did run services.msc and disabled all of the "diagnostic" services and one or two others..
On my machine there were four of them, policy service, service host, system host and tracking service.
They were all to do with MS taking stats from your machine and caused hickups.
These were all added when MS tried to force Win10 onto my machine.

I did optimise mostly for performance, not everything. I went through them one by one and tried to consider what might make a significant difference.

The key thing I found was to disable all the networking during connections during sequencing as they tend to cause 'glitches', pauses in the smooth running.
I also then disable the anti-virus program when I'm off line, so it doesn't interfere periodically.

I use the MS recommended settings for page file and have max and min the same, as I recall.

BUT, it's totally up to you what you do.
I'm not an expert here and I'm not in any position to advise you.
If you make a mistake I'm not in a position to help.
Try searching around for tips on optimising Windoze for audio.
There are several places like sordum.org which offer utilities to help with the process.
My experience was very much trial and error process.
Always make sure you can retrace your steps in case something doesn't work as expected.

P.S. If you decide to go with GPO5 it's well worth while downloading the pdf format manual for GPO4 from the lnk below.
If you can, try printing out and learning the parts about what MIDI controls do what with the different instruments.

www.garritan.com/user-manuals