Postybirb is a great tool; all log-ins are stored client-side, without the dev's server ever seeing them, so on that level it's safe. I do basically all of my posting with Postybirb, it's a lifesaver for multiple galleries and lets you queue stuff up in advance.
For Twitter posting, just be aware that it's an awful hellsite designed to be awful to use; you can't link or use hashtags because it'll reduce your post's visibility, and you need to keep the text short for the same reason. Also, it and all algorithmically-driven sites favor people who are already popular, so don't beat yourself up too much about it.
For gamedev stuff, I've heard that Facebook has good ad hit rates once you have something more visible to show? Don't know myself, I refuse to use the site. For actual vn development tools, Ren'py is excellent, it has a really low barrier to entry for basic stuff (and i'm saying this as someone who really struggles with programming). Ren'py also has its own forum, which is good if you want to look for more advice (some of it may be outdated just bc it's been around for ages, but the more general advice and recent posts should still be helpful). Steam charges to post to the storefront and is from what I've heard just generally not great to small devs, so just... be aware.
e: Oh, I forgot to mention that I'm pretty sure Tumblr also removes posts with links from its search due to a longstanding botting issue.