http://kael.civfanatics.net/files/ModdersGuide.pdf
Old (and for Civ 5, but BE is almost the same) but has both, general information as well as the whole process of creating custom Civs.

Other than that, Civfanatics.com has a ton of guides as well as a forum where you can ask for help when you're stuck. Again many of them are for Civ 5, but as long as it's not BE-specific stuff most of it still works for BE.

Old, but still relevant, as best I can tell. I notice that civfanatics hasn't even put up a section of the wiki for Civ BE yet. I'm hoping that they do. In the mean time, the V section should provide quite a bit of help.

Likewise, you might find the following to be helpfull.

http://modiki.civfanatics.com/index.php/

Within that, the following page is the most detailed explanation of what all the different entries are actually for:

http://modiki.civfanatics.com/index.php/CIV5Civilizations

I noticed that the BE public is small compared to other civs. You write something and no one write you at all lol Is like BE was kind of dead :(

Certainly not dead with 6k player peaks, but it's quite obvious that most people prefer the Civs that had way more time to get polished.