A track is a collection of MIDI events. Each channel event (an event to which a channel is applicable) can have any channel value from 1 to 16.

Sequencers or DAWs, that use a proprietary file format, might allow you to override the channel of events in a given track, but that is specific to the Sequencer/DAW, it's not part of MIDI.

Similarly, a "global channel" is a concept implemented by a Sequencer/DAW or a MIDI device, but to my knowledge there is no concept of a global channel in the MIDI specification.

Cheers
Eddie

(1) Channel vs. Track
MIDI allows a "channel" number to be associated with each note sent down the cable.
You can have 16 different channels mixed together on the same cable.
The "channel" is then associated with a particular "patch" (instrument sound) by the MIDI "program change" command. General MIDI provides 256 sounds; some workstations and software may provide even more, which can be selected by supplementing the "program change" command with a "bank select" control-change command. (Typically channel "10" is used for a "drum machine", where each "note" represents a different untuned percussion sound.)

If what you mean by "track" is a track in Logic Pro X, that represents a particular line of music--
the analogy is a "track" of an multi-track tape recorder, which is what people used before computers! Think of it as a "staff" in a score.
So when you set a "track" to a "channel" to , you provide a mapping between the notes in that track and an instrument sound on your instrument, and you can sound 16 different instruments at once.

You should consult your Stage 2 EX documentation and the Logic Pro X documentation
to learn how to associate particular MIDI channels to particular Logic Pro X tracks,
and also how to associate sounds with channels,
and how to associate the corresponding MIDI channels to particular section of your Stage 2 Ex.
As I understand, your keyboard is quite flexible regarding assigning MIDI channels.
You should have a setting that allows the Stage2 Ex to receive on all 16 channels, which is the typical setup for MIDI-in on an instrument.
To input to the computer, set the Logic Pro X track(s) to accept data from the same channel(s) as you have the Stage2 Ex set to transmit on.

(2) Is there a limit to number of tracks to a channel?
Whether there is a limit is a question for Logic Pro X. The idea is that each "channel" will be a separate instrument.
So for example, if you are doing a choir score with 4 separate SATB tracks and 2 separate tracks for LH and RH piano, you might assign the four choir tracks to the same MIDI channel and instrument "Choir Ahs," and the two piano tracks to a different MIDI channel with instrument "Acoustic Grand Piano."

(3) If you are asking about the Global MIDI channel on your Stage2 EX, you would best consult someone familiar with that instrument, but it seems to me that this channel imitates playing the keyboard. In other words, data from computer to keyboard is interpreted as if you pressed the corresponding keys on your keyboard, using the current sound setup on your instrument and ignoring program change info from the computer. Similarly, it transmits all the keys and controller changes you play, so you can make a "faithful" recording of your performance.

[I must confess I don't know how your instrument or DAW implements "layered" sounds;
it would seem to me this would require 2 channels, one for each sound; I'm not familiar with a MIDI function for "layering", or activating two programs at once.]

A "global channel" is a concept implemented by a Sequencer/DAW or a MIDI device.
Global channel on hardware MIDI devices works like default channel on which device will listen/send incoming/outgoing notes and events.
A multi timbral synth/keyboard can play the note within different channels according the midi signal.
But when you play a note on the keyboard, everything will be sen on "global channel"
Some synths has single/multi mode can override global channel by selecting the channel on multi mode.