I follow a few creators on kinkycats.org . Some sell, some don't but the instance seems very friendly to it, where creators boost each other.

Technically I don't think it's against the rules of FediNSFW to self-promote, only to do so in comms that prohibit it. Most comms here are intended for non-commercial things (such as this one), and most people are here for that kind of content. However, it would probably be fine to make a community dedicated to commercial (paid) content, so long as it doesn't get spammy.

to my knowledge, not anymore. (there used to be Switter, but it died a while back.) tbh, speaking from experience, your best bet for using fedi to get buyers is to basically do what you've been doing, and integrate yourself with what i affectionately call "horny fedi". keep links out of the main post and in a reply instead (if you include them at all), so the post itself doesn't feel like an advertisement, and participate and interact with others in the community, boost their stuff, etc. there's a general understanding on fedi that "we are the algorithm", so by actively participating in the community, people will naturally share your posts around if they like them. mention your services and include your links in your bio and/or a pinned post (if applicable, if that's a feature the instance's software has) and people who are interested in buying will come to you. and honestly, horny fedi is sex-work-positive enough that you'll probably get people sharing around your post with your links in it too!