First, YOU are the one who is talking no8, no 10 AN, not me. I didn't even mention the 'S' word. A new OEM quality STEEL 3/8 line is dirt cheap compared to anything AN or stainless. I think you'll find that AN fittings prices escalate dramatically between 6, 8, and 10
I think the OP has made it pretty clear that he's not building a huge monster. Comon, keep it in perspective, eh?
1/2 tube is much more difficult to work with than 3/8, especially stainless vs steel. I just don't see it. Sorry. And finally, I doubt from the way the OP describes,...........doubt he will ever need anything larger than 5/16!!