It depends how much you like reading
The 3D work has been a pretty open process, as other than a few PMs here and there, it's basically been entirely coordinated through these forums - so if you read
the entire of the 3D Development board, you'd pretty much know most of what anyone else does
For a smaller level of reading material, I'd recommend looking through the
tutorials on here first. These should include some information about the layering and structures, and also some downloads for template files (please tell me if any links are broken). There's a part 2 for the rigging which I should really get round to doing, but you might be able to work things out yourself by looking at what's there so far and then testing a little yourself. If you're able to read Russian, or interpret Google Translate clearly, there's a load of information on fonline.ru as well.
There's a couple of SVN repositories which contain things "done" and "half done". These should be linked in the tutorial thread.
Regarding what models to work on, if you look at
The 3D Armour Development Tracker, that's pretty up to date. There might be a few in the suggestions thread, but I'd try and focus on the existing ones first.
I'm currently testing some things with the tribal and vault textures, but if you scroll down a little the male robe model certainly needs doing (unless Pistacja is still planning on doing this). There is a female one which should be tweaked for this. Some of the armours might be tweaked in future (I'd certainly like a 2nd go to improve some of the ones I've done), but essentially if it says "missing", it needs doing. If you can create the look by texture alone then do so. Looking through the existing ones should give you a rough idea of how they've been put together.
If you have time to learn rigging for these models, then that'd be awesome - there's a lot of rigging work that needs doing. As said, it should be a little easier once I write that tutorial, but if you're a fast learner, if might be quicker to follow up until "rigging a hat" and then just playing yourself until you make sense of it. If you don't have time for the rigging, don't worry. Filling those "missing models" is still urgent and important.
Hope that all makes sense to you. Feel free to ask any questions if not