Here are basic stuff not found in the doc.
I put rants in italics so you don't have to read them if you just want somewhat useful info.
-Build generates some files in the MODS folder. It actually generates a folder, with a version number (that must be an integer and cannot be the usual integer.integer format).
This output is not a civ5mod file. (This may qualify as a rant.)
It's also not possible to set the output directory because it's already where you want it (except you can't share it with other users on the same computer except by copying it and moving away, of course, but you don't want to share data on a personal computer anyway).
-To get a civ5mod file that can be uploaded, you must zip the output of the build command with 7zip, rename the .7z file into a .civ5mod file and then you can start uploading it.
There may be a way to do this from ModBuddy but I haven't found it. I think I haven't yet mentioned I hate IDEs so I'll be doing that right now. I hate IDEs.
-When uploading, do NOT forget to check the categories you belong to or your mod will never be found in the jungle.
Although you can preview data, you cannot change them at this point and apparently have to close the whole Online service window to fix them in case you missed something.
I've been unable to preview the homepage despite it being in the info file. Maybe it's jsut the preview, or something is broken?
-When you check your mod in the mod browser, if you see that the date of the mod is TOTALLY false, don't panic. It's normal, you're just not in the good timezone. You may be a filthy foreigner for instance. Of course, checking it's the version you uploaded 5 minutes ago and not the one you uploaded 1 hour and 5 minutes ago is very problematic, but you should have changed the version number. Also, if the category you put your mod in doesn't appear, don't panic. It's hopefully going to happen sometime in the future. Don't start ranting like me because noone will be able to find your mod, for instance.
-Finally, if someone could explain me how I can reuse the .sln/.vcproj of another mod when these aren't published/part of the civ5mod, I'd be really interested. Maybe it could be interesting to just see how someone organised their work to just get an idea of how to manage it. Maybe you'd like to make a variant of someone's mode and it'd be easier to tweak it rather than make a modmod. It's probably a bad idea, but I'd really like to have the option.