yeah, basically if i am creating a sequence, say i'd like to add some strings, can i just move to a new track and record/overdub whatever i happen to play on a keyboard, and those sounds will be saved as part of that track, without the need for me to sample those string sounds first?
What you will be recording is the midi data of the notes you play. You could then get the MPC to play those same notes but using a different keyboard sound. The sound itself won't be recorded into the MPC. So, as long as the keyboard is part of the same studio set-up as your MPC, & you remember what sound you wanted that MPC track to play (& you should probably name the track with whatever the keyboard patch is called) you will get the same sounds working together each time you load that MPC sequence & program.
But ..... if you just have an MPC & you take it round to your friend's studio because they've got a Triton & you record some midi tracks with that, you won't get to hear those when you take your MPC back home unless you take their Triton home too, or sample the Triton parts.