1) My unit size

is $70-100 for something i feel pretty confident about, $40-50 for sides and such. But everyone's unit size varies, it's just a nice way of not explicitly talking money. Some guys will, like Chainsaw and occasionally GooRoo.
Everything is relative re: odds. The best way to think of -375 is that the break-even % is 78.95% (use
this). Let's say you're making 100 different $1 bets on an event that you think will win 90% of the time. 90 of your bets return 0.266 ($23.99), and 10 of your bets lose $1 (-$10). That's a 14 unit yield over 100 bets, which is pretty damn good.
Granted, at 78.95%, there's not much space between you and the ceiling. It's tough to find bets that are going to yield a profit at long odds like that. They're also pretty miserable from a psychological perspective, as there's only relief if you win.
2) Parlay odds depend on what you're parlaying. Parlaying two -110 games yields +260, but you can parlay all types of odds. People typically like to parlay a couple of underdogs to get a decent payout instead of laying $1 to win $.50.
Parlays are an accelerant: If you're making bets that normally wouldn't return a profit if you were betting them straight, you'll lose money faster if you parlay those games. However, if you are making +EV bets, you will win money faster with parlays.
3) 100x yes. There is very little homerism in the FFAWT. Everyone knows who everyone else roots for, but the rah-rah #### isn't really welcome in there.
4) *bonus*: Tail anything that GooRoo posts.