Hi Carlton –
You’re right, 720 30p is what you want. Computer monitors are progressive, not interlaced.
As far as encoding, try experimenting with the YouTube presets in Compressor. When you’re done the project, export a brief clip to test using various encodes and find which works best in all the places they decide to use it. Sounds like you may be able to get away with just one encode for YouTube and link to it with Facebook and Twitter.
Good luck.