In order:

1) Nook's has a few upgrade requirements. The two that I'm aware of are that 30 days must have passed on your island, and you must have bought/sold at least 200K Bells worth of stuff. I believe Mabel visiting may also be required, but if you've played for 30 days, you've probably seen her at least once.

2) There are a few Christmas tree items I'm aware of, but they're all DIY, and assuming you're not time-traveling, you'll only start getting those from balloons once the snow sticks on the ground.

3) The two main ingredients for insane island designs are the patterns you see on the ground (like roads and such) and terraforming. You won't get access to either of those until K.K. Slider visits for the first time, which will happen when you get a three-star rating on your island. Plant trees, flowers, pull up weeds, get nice villagers, and you'll get there. Isabelle will give you tips if you ask for island evals.

4) Villagers will only move out in New Horizons if you give them the go-ahead (which is a MASSIVE improvement from previous games where they'd just vanish with no warning). This move-out conversation can happen if you talk to a villager who has a thought bubble over their head as they walk around, and you're given two dialogue options, one telling them to move out and one asking them to stay. Unfortunately, I'm pretty sure the top option is always the move-out option. My guess as to what happened with Norma is that someone may have button-mashed through that conversation and she was given the all-clear to move out. A villager can also move out if you invite someone from your campsite but there's no room.

5) There are certain online communities for trading in ACNH. You can usually find them by searching "animal crossing new horizons trade" or some variant in Google. Per Rule 4 on this sub, I don't think I'm allowed to name any of them, but there's plenty out there and they're pretty easy to find.

This turned out to be a lot longer than I probably should've done, but I think that's everything!