1: What is the equivalent to .2da and .tlk files, if any? Can I edit such files?
Brushing off some NWN2 cobwebs, I would say:
The "Translated String Editor" is the equivalent of the .tlk files. It's the place where things like new book entries, tooltips, tags and many other string references are stored. You can edit this from within the editor. See the
wiki page for some more info.
I think most of the content that could be found in NWN2 2da files would translate into lsx and lsf files, or stats files that end up as generated text files. These all get packaged up into *.pak files. The editor provides a user interface for modifying many of them, but not all. For those that need to be edited outside the editor, there is a
pak extractor that can extract them and/or create new packages. This isn't my area of expertise, but I think it's roughly equivalent.
One item of note is that DOS2 handles merging multiple mods better than NWN2 here, since there is no need to merge 2das of the same type when wanting to run with multiple mods (multiple HAKs in NWN2 terms). The only time there is a conflict is if you are actually modifying the same named entity in two mods, in which case whichever one is loaded last wins.