I've been doing this about a month, but I can tell you that the throat hit is great on the 510, at least with 36mg juice. Forget about the carts the kit comes with - if you get into this you'll need to order blank (empty) carts and liquid anyway.
As for sites, you'll do the best on price from eastmall or ruyan, but a lot of domestic sites will ship faster (like 2 or 3 days) for $6 or so. esmokeytreats and nuvape come to mind. altsmokes too. order the basic kit, some blank carts and some liquid to start, if you like it get some spares (atomizers and batteries), also a PCC and a passthrough (if you're at a computer all day). go hardcore with a syringe to properly load the blanks.