pjw77

Hi folks--
I'm restoring a 1983 Trek 720. The bike was in disarray in the corner of someone's garage when I bought it. I've got it all stripped down to frame and components, cleaned everything up nicely, did a little paint touch up, and am now starting to think in detail about starting to build it back.
The current puzzle I've got is the drive train, and it's only a puzzle because I just don't know much about it.
Here's the "known" parts:
* I'm going to use a Suntour Cyclone GT rear derailleur
* the bike came with a Campagnolo front derailleur
* the bike came with a Sugino AT triple crankset, with a 50-tooth chainring, a 45-tooth, and a 28-tooth "granny". I plan to use all that.
* came with Suntour bar-con shifters, which I plan to use

The bike came with a 5-speed Regina freewheel. I'd like to replace this, but don't know what I can/should be looking for. Can I put a six-speed freewheel on? What about a seven?

I also don't know what I should be looking for in a bottom bracket. I guess the main thing to consider is total length?

Thanks for any help/info. (And if this is the wrong place for this post, please let me know).