Welcome Cheez! You have received a lot of great advice so far as we all have on this awesome forum. It sounds like you are getting a handle on what your plan of action will be in the beginning and down the road as well. Allow me to offer my support for the eGo-type of 510 system to start out with... Either the Joye or the other clones of it.
I made the decision based on the eGo's long-lasting battery, fine overall performance, universal availability and reasonable price. Seems that everybody carries the eGo in one form or another. It really peeves me to see "Out Of Stock" frequently emblazoned on a vendor's website - just when I've got a small window of opportunity with ready cash to BUY NOW! Grrr! You will not have that issue with an eGo.
You will also find that virtually EVERY vendor on the planet carries aftermarket 510 atomizers, cartomizers, batteries, cartridges, widgets, whatnots and stuff like that there... all in-stock and ready to ship. Some humongous cartomizers are available for those marathon vaping sessions too.
As far as leaking is concerned, the only time I had a cartomizer leak was when I got real wild with the juice in the first few days of using them. I figured "more is better right?" so I filled that goomer right to the brim and jammed the little white cap on. Naturally, the force of pressure on a liquid will not be denied so it squirted the precious juice out the other hole onto my favorite Sunday go-to-meetin' trousers. Reddish liquid, tan pants. Not good. Lesson learned. Been fine since.
After you have gained some insight into the whole new world of vaping, you will be in a better position to determine the next step you might want to take. There is a bewildering array of vaping devices available on the market - all of them have a loyal following and all for very good reasons. They seem to work wonderfully well but are they right for you? I dunno and most likely you won't either right now. I'm learning that taking the baby steps first with a simple gadget is a good way to be. The eGo gets my vote on that score, maybe it will for you too. It just works like crazy! Later on? We'll worry about that when the time comes.
Best of luck!
Oh, just remembered one more thing...there are times when it is handy to have a very tiny PV for stealth vaping. The 510 has that covered as well. Just buy a couple of the standard batteries or a mini box mod plus a charger. You can use all your existing carts, attys, cartos etc. without fiddling around, keeping track of incompatible, proprietary connectors. just another plus!