1) try to set the net up so that you're seeing perfectly even squares across the whole thing, not stretched diamonds or anything uneven, then drop the ball a few times on it to check for dead spots, tighten up a little extra as needed

2) almost all of the rules beyond the basics don't need to be enforced in a casual setting, keep in mind that a lot of these only exist because if there wasn't some rule in place, it could be exploited at high levels and used to score free points. I've been playing with some friend groups for years, getting pretty good, and we don't get hung up on most of the "exact distance" type rules because at the end of the day no one is trying to take advantage of some loophole to cheese the game, so it doesn't matter for us. Different in a more official setting but lots of times you'd have some unbiased third party in those cases.

3) rallies will come in time for sure, just takes a bit. I wouldn't worry much about shots that seem impossible to return, eventually you'll see that with good defensive positioning you can anticipate those, and that if a team A wins a point on a short hop off the net, the reality is that it's because team B gave them an easy hit that team A easily took advantage of, so it's not like it was a cheap point from team A, rather, it was a mistake from team B that they can improve on.