There is loads of info on google and you can even buy mixing kits..
Nice guide here
http://www.e-cigarette-forum.com/forum/diy-e-liquid/218802-guide-making-your-own-e-juice.html
Mixing kits here
Mix your own e-liquid | nicotine solutions | diluents | flavour concentrates.
But really, since I found Isle of Custard, I wont be making my own again, 100ml for £19.00 of the best juice I've ever had, why would I, it is just incredible juice
Isle of Custard by Mike -
Isle Of Custard E-Liquids Isle of Wight
And where I'd buy my devices ect, KingZing, Nick is a great guy, good prices and the best customer service I've found for a long time,
Kingzing -
KingZing Electronic Cigarette Store
Basically for me, Captain's Custard Donut juice 70/30 6mg with the Subtank mini 1.2 coil at around 16 - 20W on the Istick, vaping heaven, I wish somebody had given me this advise, would of saved me a whole load of brass.....
I'm with you on the 30W but its personal preference, the 30W is enough for both the 1.2 and 0.5 coils, I only use the 1.2 ..sometimes at 16W, 17.5, never higher than 20W, I enjoy a cooler vape so the 30W was overkill to me....the only reason I got the 30W is because they added some features, like locking the device, improved connector and most of all, they changed the top so the Kanger Sub mini fits perfect...or any 22mm tanks..it had nothing to do with the extra wattage.. but that's just me.
EDIT - Your in the USA - Stupid me..I'll leave the links up though, useful info..