Ran out of bars - is there a limit?

[dflat]

I can have 12 staves... Is that normal or weird?
Plus, one time I imported a song and it had 3 extra measures at the bottom which were uneditable ...

12 systems is the maximum. Some long songs need it.

Not sure abut those extra measures you mention. Do you have the original? Yes the best way would have been to do what you did to resolve it.