It takes longer to call a sub to execute some code than it does to execute it
inline.

that said, it is not a significant performance problem and the benefits
probably outweigh the penalties.

The only limitation I am aware of is that if you exported a module to a bas
file, the size of the bas file should be less than 64K.  This isn't a
published limitation, but many have stated it as a rule of thumb which if
ignored can cause problems.

That really has no effect on the number of procedures which I am not aware
of any limit.  

At the same time, from a maintenance standpoint, I suppose you can go
overboard.