its actually a section under the "Tips and Tricks" forum called "DIY Liquids" i believe. anyways, the flavorings they primarily use are Lorann's and just make sure it is water soluble and you may want to avoid colorings, as they might stain your PV and perhaps your lungs (though there isnt any hard evidence one way or the other for the latter). if it has oil in it, avoid it, and as far as alc content, I dont know about that one, several of the recipes i've read seem to contain flavors with alc in them, so i guess its probably fine. anyways, there is a GREAT wealth of information in the DIY E-Liquid forum under the tips and tricks area, so check there and have fun!
-Ben