Reply to tips and tricks for modding: what do I need to know?

I'd like to start out by modding a nano-something, 50 bucks Canadian, you can hardly buy arcade buttons for that lol.

What I'm interested in right now is making a 3x8 grid for cue point chords. I'm fairly certain I could buy 2 nanopads and usb hubbing them (other thread). I am also fairly certain that this could be done by replacing the case and buttons with Sanwa buttons. However, the nanokey has enough buttons right off the bat.

The things that I'm wondering about are:

Velocity-sensitive- does this make a difference? can the velocity sensitive keys (nanokey) be simply swapped for sanwas?

I am under the impression that the nanos come with software for doing all of the midi mapping stuff already, so I would not be disappointed if people ended up disregarding the rest of the message and telling me to just get a pre-fabricated digital music controller. However, because I'm curious, if someone could write out an explaination of things? if not writing it yourself, I'd be happy with directions for finding answers in a book or something, I've tried to do my own research but there doesn't seem to be a lot out there.

So: possibly useless questions:

what is the difference between analog and digital buttons? (am I seriously confused here?)

can random midi keyboards and the like from garage sales be modded and used in software? (mostly for practice, I have 2 little brothers that I'm sure would be interested in this sort of thing)

how can you tell what can be modded when shopping (I have tried my hand at circuit bending, and there are lots of midi things in garage sales and on kijiji that are cheapppppp).

I feel like the controllers are easiest to mod, I'm scared of anything that has a built in computer chip with a sound library. However, lots of the cheap midi ones have sound libraries. Does this cause problems or can the sound library be replaced with a usb cable? Also, if the thing needs an external power supply, I believe it's safe to say that I should stay away from it (learned from circuit bending), but what about batteries? Is there any current that could fry a midi to usb converter or the computer all together?

I don't mind reading or learning or reading from a website, I just believe you guys might know the best links to try out.

Thank you so much for reading my novel. I'd like to really get into this.