Those are good questions, and deserve their own thread. They have been discussed in the past, of course, things do change, but the basics stay the same.
First determine what this rifle will do - what range and target is intended. That will clear up the 5.56 vs .308 quickly, as they are aren't suited for doing the exact same thing. Once you drill down thru the subsequent decisions, you then get a feel for what features, and finally, who offers that type rifle.
And if you get that figured out by Thursday, PSA will be more than happy to take your order.