On tumblr: I've used it for about two years now, on-and-off. My blog is 99% shitposting and the occasional painting or political post - asides from an NGE phase I had last year (a decade late, well done me), I feel quite weird stepping into fandom, I've consciously avoided it for years.
As for using tumblr, there are lots of different ways of approaching it - some see it as a social network, but I tend to view it as an online depository. I tend to think of it as personal collection of beautiful pictures, amusing .gifs, good jokes, etc. It's meant I've managed to step around the worst of it.
If there's any rule I'd put forward, it's never send online hate ever, use your anons for a task for good.
Some see it as a social network, and you can use it that way, but Tumblr is more made for sharing than real discussion, so while you can connect and reblog and have about 10 nested reblogs with comments and all that, it's clunky. You can send comments on posts but they're really character limited. The idea is really to reblog and comment there as the way to communicate, or use Asks.
Sometimes I don't want to reblog an entire thing but I want to more than Like it, so I'll leave a comment if the person has comments open (and you can NOT have them open). it's a bit like a maze at times, so i tend to stick to sharing but it depends. I have a really low post volume so I just reblog things I really like or feel something toward.