4-5 times a day is very normal. And it also sounds like he needs longer walks. Not sure what breed you have but dogs should ideally have around 30-50 minute walks 4-5 times a day. As for the smelling areas, they're looking for territory marking spots. Walks are like the news for dogs. They'll smell around finding what other dogs have been there and leave marks of their own.
Your dog's behavior is very typical, and it doesn't sound like the dog needs to change, but rather that it does need more walks. If you are a very busy person, I'd suggest occasionally hiring a dogwalker. The winter cold is unfortunately just something that comes with having dogs.
I think it is absolutely fine. Most of the time the communities are on a .ml instance, or modded by the worst people imaginable.
Make many communities and let the inferior ones die. This is good for Lemmy. Just don't copy the same posts to your community, as it'll fill the front page with duplicates, which is detrimental to Lemmy.