Is there anything out there (e.g. wiki or forum info) describing what the different file formats in Fallout 4 are for?

I do not know of a comprehensive list. Which formats were you wondering about? Also, Fallout 4 has many new formats and I'm not sure we know what they all are yet.

https://github.com/TES5Edit/TES5Edit/commits/sharlikran-fo4dump source code for plugin format

https://github.com/jonwd7/nifskope/releases/ nif.xml for nif format in general, and https://github.com/ousnius/BodySlide-and-Outfit-Studio source code for clothing and body nifs particulary

https://github.com/jonwd7/bae source code for BA2 format

http://svn.gib.me/public/fallout4/trunk/Gibbed.Fallout4.FileFormats/ source code for materials BGSM and BGEM format (they could be renamed json also).

Usage of channels in textures description you can find on Nexus forums.

There are no FO4 tools yet for behaviour files, other misc files I don't know, but some of them like *.sclp are json.