I'm not a web guy, but I reckon an actual working site would be better.
If you just had screen shots people might wonder why, maybe you can't actually build them. See what I mean, maybe a mixture would be so bad...
Alot of the answers to your question, have already been asked before on the forum.
Search is your friend. lol, there is alot of good advice on here, just a case of finding it.
But you generally seem keen which I like in a fellow designer, so stick at and dont let your designs go for cheap
That's the problem if someone offers to work for free. As soon as the customer hears "for free" they try to squeeze you as much as possible. I experienced that when my brother offered a company to help them coming up with some custom designs and designing the whole page. He chose to do it for free, so that it could become part of his portfolio and they were very demanding.
Logic will get you from A to B. Imagination will take you everywhere. - Albert Einstein