Batch size vs. fermenter size question.

Hey guys, noob here. First off this has to be the best forum on brewing that I've come across. Now for the question, I'm planning to cut a 5gal. extract kit in half and have a 3&1/2gal. bucket (scored from Festival Foods bakery dept.) that I planned to use as my primary. Will that be large enough or should I just go with a 5gal. size one. Thanks.

You should have enough room to make a 2.5 gal batch. Maybe just as a precaution you might want to use a blow off tube but as for the brew it will come out just fine.

the other question would be what kind of beer and what kind of yeast, heavier beers and certain strains of yeast may produce a more robust fermentation with a lot of krausen.
A simple pale ale with lets say safale us-05 for example, fermented in the mid to upper 60% range you'll probably have no problem at all.
A few drops of Fermcap will also keep Krausen at bay and allow a smaller headspace in your fermenter.

Caribou Slobber from Northern Brewer is what I'll be using menerdari, actually I measured out that bucket just now and discovered it holds a little over 4gals. so that should give me plenty of headspace. I'll use a blow off tube as geim32 sugested. Cheers