Aha!! It's all coming back to me now... When I first went to your website, I noticed that you were looking for a better description for your Vanilla juice, but I guess the one I sent in wasn't good enough, even though it was pretty much taken directly from the
Book of Spices as I recall... LOL!!
Although I have not tried your Vanilla, I agree with
bigbloom about trying to find a really good one, as in a true vanilla bean, since most of them seem to taste like cake frosting or imitation flavoring. I have also had a hard time finding a deep, rich Chocolate... I like that you have all single flavors, because that is the true test of a juice, and is all I really get because I like to mix my own concoctions... Ha!!
Anyway, I have entered (and won) a fair amount of contests here on the ECF, and what I have found is that the ones that are the most fun are not necessarily the most beneficial to the supplier as far as generating more customers and/or traffic to their website.
Ripple suggested having people go to the site and pick a flavor, but I might even go a little bit further and have them pick 3, since you offer sample sizes, and the prizes could be that they would get those flavors. That way you would get a better idea of what kind of flavors people like, and they would also get to sample more of them, rather than just giving out one big bottle. or you could do the same with 2 15ml bottles... You could choose the 3 winners by Random Number Generator, which would level the playing field, and make it easier for you as well.
As far as what brands or mods to carry... it all depends on the type of customer you are aiming for. Whether you want to offer kits for a newbie who is just starting out, or something more advanced for the seasoned veteran. I started out with a Joye510 kit, but for 3 of my friends that I helped to make the switch to e-cigs, I recommended a KR808 because of the ease of using cartos instead of the atty/cart combo and longer batt charge life... and 1 of them didn't really want to be bothered filling the cartos and there are plenty of pre-filled available.
I also have a VGO 900 which uses all of my 510 stuff, and as far as the 901s go, the Rivas come in both 510 and 901 connections, so those might be a safe bet... plus you could always carry adapters, too. Start small and you can always add more stock later as the demands grow...
Hope that helps, and I can't wait to see what you come up with!!