There are two developers, @jps and @wbond that work on the core of Sublime itself. Besides the application, it also ships with a set of packages that provide syntax support for a variety of languages. That aspect is online on GitHub and open to pull requests from volunteers in the community working together, so in that case there are many people working on things.
Quite a few (too many to list ) but for a general overview ST3 is under active development but ST2 hasn’t been updated in years. Despite it being referred to as beta
, it’s rock solid stable for production work (unless you’re using one of the development versions, and even then they are pretty stable as well) so I wouldn’t let that scare you away.
At this point the only real reason to use ST2 over ST3 is either because you absolutely require a package that doesn’t have support for ST3 or because you’re ultra paranoid of labels like “beta”. If you buy a license right now, you get access to both versions (including ST3 when it is “officially released”).
The only difference between the trial and the registered version is that every so often after you save a file you get a message dialog reminding you that if you like the program and find it useful, you should register it, and that the title bar and about box remind you that it’s unregistered.
Aside of that it’s 100% identical to the licensed version (no missing/reduced features).
This I can’t comment on, as I’ve never used it. This search on the forum pops up some presumably relevant material. The first hit in particular is probably the most in depth of them, at first blush.