Is it a good idea to write a larger than expected project report?

If I say "3 or 4 pages" and get 5, not problem. If I get 12, my first reaction is to give minimal grade, for not following simple guidelines. If I'm in good mood, I'd read it (unlikely, term's end isn't a time for jollyness ;-), and if it really dazzles me (no rambling, no unending tables that could have been summarized in a graph or two, does the work asked, and goes far beyond it in useful direction) I might even give some extra credit (and bookmark you for later). If just longwinded explanation that could be summarized in 3 pages, again fail.

You say, never said - how do you know?

In any case, if 4 is the limit, write 8 pages, cut to 4. From experience, it will be much better this way.

It depends.

In my courses, the professors usually list a max page limit but no minimum. I talked to one and he said its because he doesn't have time to read 50 students' papers if they're all too long and he has had too many students that ramble.

My suggestion is to tend towards following the directions. If that isn't enough, then just ask the professor. A one or two line email could solve this!