BMXes are mainly ridden out of saddle, so size isn't that important. but it's probably on the small side.
64
Yes.
Yes.
64 and 121 share the common factor of 1.
They are not a direct bolt on but they can be made to fit.
I am still looking
The average iTunes song is around 8 megabytes, so about 8,192 songs can fit on 64 gigabytes.
9, remainder 1
64
There is no number that can fit evenly into both numbers.
very possible.
Exactly 32 times