Welcome!

Where do I go to see comment or post replies?

There is a little chat symbol next to posts to go directly to the comments.

Is there voting? Is content that is not welcome discouraged in any way?

You can click the little 'hubwheel' on the top-left corner of posts to show that you appreciate them, if this is a post, it will 'Share' it to all your followers and if it's a comment, it will float closer to the top in that thread. You can hubwheel as many posts as you like.

There are no moderators or admins on Hubski in the sense you get them in Reddit, users do all the filtering. So you're free to post whatever you like, and if someone doesn't like what you're posting, they can click on your name and mute, filter or hush you(Mute stops them from posting on your posts, filtering stops you from having to see what they say and hushing just sorts them to the bottom of every thread.) personally I find this system much better than reddits.

Is there text formatting?

Yep! click 'markup tips' on the top-right bit of a text box. The formatting is mostly the same as Reddit's, except with some differences such as \> being replaced with surrounding quoted text in '|'

If I have niche interests, how would I go about cultivating a community to explore them? (Aka /r/abrathatfits, /r/trollxchromosomes, etc)

Hubski functions similar to Twitter in this sense, you post whatever you want whereever you want to. Because of the follower system, the site consists of social bubbles based off who get along rather than only people interested in similar topics(You can search tags to find people of similar interest, but you're not forced to spend time together because of your similar interests)

A while ago I asked a pretty niche question about OpenGL(A computer graphics library) and rob05c answered, in the future I can mention him in OpenGL questions and he'll get an alert, and if I see an OpenGL question that I don't know the answer to, I can refer them to @rob05c then too.

Cultivating communities around niche interests isn't really possible, you can only really cultivate communities around people. That's why I still use reddit(Might switch to voat.co if it gets more popular). Hubski isn't meant to replace Reddit.