I am trying to dig my way through the various DAW's on offer and think I might not need anything complicated for what I want. I would like to use my Ipad Pro if possible but that is not a deal breaker - I could use a Windows laptop.
All I want to do is to play live sounds using my keyboard or another MIDI source. I don't need all the tracks or songwriting. I don't need to tune the individual parameters of a sound or add any effects. I just want plug and play sounds. I just want to be able to import some addition Vst samples so I can pay for really good quality live sounds. Is there a piece of software out there that will do that?
You are looking for a standalone vst/vsti host app. I don't know if there is one for iOS. But there are some (not a lot) for Mac and Windows. The problem is that vst/vsti is a plugin technology oriented to big DAW applications, which are vst(i) hosts in addition to record/edit/production tools.
But if you open your mind a little more, now that you realized that you don't need a DAW to enjoy your music freely, then maybe you discover that you are looking for good realtime MIDI Soft Synthesizers, without limiting yourself to VST(i). Maybe you are even disposed to explore Linux too.
There are a number of apps that will do what you want. GarageBand should allow you to play your keyboard with a MIDI controller keyboard. Try doing a websearch on iPads apps with MID keyboard controller. That should give you a number of apps.
Then you should just need a iPad camera connection kit which is just a USB A socket-to-Lightning connector so you can plug in the USB cable into the iPad.
Most apps should work right away. There might be a little setup involved to get the knobs mapped but if you want to play piano, it is likely plug and play.
Another options is to get an audio interface for your iPad. Just one example is the iRig Pro IO. The older version is the iRig Pro. Both have MIDI In so you can use the MIDI DIN connector.
Whatever you find, make sure it is supposed to work with your version of iPad or laptop.