HGEC is a female body mesh derived from Exnem's EC. The UV map is the same, meaning textures made for EC will work for HGEC and vice versa. It's not an addition but an alternative to EC. It used to require EC because it was packaged without textures, but Exnem's are included now, making it a standalone mod.
- What are the basic differences between, let's say (to keep it simple), just the 3 body mods mentioned above (Robert's, Exnem, HGEC)?
Basically, looks. Look at em pictures, see which body you like best.
- How can I find the main files/mods (it's a bit hard to distinguish between the basic files and the tons of additions provided by other modders)
By "main files" I'm assuming you mean the files needed to install the body itself?
Exnem's EC - look up "Female EyeCandy Body Replacer" on the Nexus.
HGEC - I'd recommend installing that one with "EVE HGEC Eyecandy Variants Expansion".
Robert's female - you'll want "Roberts Female Body v12 Fixed".
Robert's male - since there's no official release for Robert's male body v5, and I'm guessing due to permission issues, there's no "all-in-one" package for the standard, average version. To set it up as painlessly as possible, I'd say your best bet would be to install "v5 Average Clothing and Armor Replacer Fix" along with all requirements.
*Note that Robert's female includes male textures for Golden Saints and Dark Seducers meant for use with Robert's male.
- What other replacers or additions (armor, clothing, weapons etc.) do I have to install?
The only thing you'll need is armor and clothing replacers. If you don't have any and you put on a shirt, for example, your upper body will revert back to the vanilla upper body, so you might get beefy vanilla arms plus mismatched hands. Sometimes clothing and armor replacers are included with the body mod itself, sometimes they're not.
Exnem's EC - not included, look up "Clothing and Armor Replacer for Exnems Complete".
HGEC - included in EVE
Robert's female - included
Robert's male - there is one included in AlienSlof's release, but it's for the v4 muscular variant - different shape and no nails. For v5 average, see "v5 Average Clothing and Armor Replacer Fix".
- What incompatibilities do need to be aware of? Especially, what about compatibility with OOO and other overhauls?
Again, you'll need replacement meshes for all clothing and armor that show skin.
Exnem's EC - support for OOO, MMM, Fran's and more are available, look up "OOO Armours for Exnem" and stuff by Axil.
HGEC - see EVE's optional files. OOO, MMM, Fran's and more are covered.
Robert's female - support for OOO, MMM and Fran's is available, look up "Roberts Female for Mods".
Robert's male - support for OOO, MMM, Fran's and more for v4 muscular. Look up "Robert Male Muscular". Nothing for v5 average yet, AFAIK. Senchan's replacers work fine if you don't mind the little differences between v4 and v5. They're certainly much less dramatic than between vanilla and v5 anyways.
Of course if you're using an overhaul that doesn't add new clothing or armor like TIE, then you don't need to worry about any of that.
I hope that wasn't
too scary.