I'm following you here. With 10 songs in one set you would have as many keys as you have on your keyboard or midi device. With 50 midi options you'd probably want to label a midi device. No if you open and close songs, then you can have the same 5 keys assigned in each song each time. If you want everything to be all in one set and open immediately, you can use a key only once.
I personally like to use 1 for song one, 2 for song two, etc. and then just do markers for the sections I plan to vamp... you can then choose to in the moment or let it play, but I dont need markers for every part of every song.