The Steam release only just came out, so it's going to take time for people to figure out everything that's changed and assemble that information into a tidy document. That being said, it's my understanding that not that much has changed within the files outside of the addition of graphics and the ability to amend preexisting files. Following the outdated modding guides should be enough to get you ~70% of the way there. From there, I recommend keeping a close eye on the modding forums and the wiki to keep abreast of all the things that are changed as they're discovered.
With all that, I should be able to give some pointers on whether the things you're hoping for are possible! (With the disclaimer that any of these things might have changed, we can only know by testing.)
- The answer to your first inquiry depends on whether you mean to change an existing creature, or whether you're making a new creature out of whole cloth. In the latter situation, you simply include the relevant tags when creating it. In the former, you use [SELECT_CREATURE:] to select it and add the tags like so.
- I don't think there's a way to make a creature only wear a specific type of armor, but you can certainly add [EQUIPS] to allow it to wear armor and wield weapons in general, and if the creature is associated with a civilization you can make your modded armor unique to that civilization.
- You can add new types of armor + define new materials. No problem. I haven't heard of any changes from the previous version, but again, anything could've happened.
- You can mod chitin to be tanned. I'm not sure if you can mod a specific creature's chitin to be tannable? I wouldn't be surprised, though.
- I don't know enough about the mechanics of creatures sites/sieges/raids to comment on this one, I defer to someone more familiar with the subject.
- I don't think live food as you're imagining it is possible in the current version, unfortunately. Only animals with the [GRAZER] tag experience hunger, and those are strictly herbivorous.