Well, you've made the right decision with the 510 IMO, and cignot is a good place to get it from. I think you'll be very pleased

Getting the liquid and filling your own carts is definitely cheaper and better than using the pre-filled carts, but be sure to buy some dry carts to put the liquid in.
As for the liquid, there are a few things you should know. Most liquids are PG (propylene glycol) based, but some are VG (vegetable glycerin) based. Some people have unpleasant reactions to PG and so prefer to use VG. I'd say most people are fine with PG so I'd start with that, since there's a bigger selection to choose from. I, myself use PG liquid (RY4 flavor from
MyVaporStore.com) and mix it with about 1/3 VG. You can get VG at any health food or supplement store; just be sure it says "UPS" on the label. I buy the highest nicotine liquid I can get, so mixing in the VG reduces the nicotine content and gives me more vapor (VG produces lots of vapor). You can also get a high nic juice and some 0 nic juice and mix them together until you find the nicotine level you're comfortable with.
A word of caution: cignot sells ecoPURE e-juice, which is VG-based. I love that it's VG, but I think it's strange-tasting juice. They had a problem recently with a batch that wasn't mixed properly and tasted horrible. I was assured those problems had been corrected and I would be receiving the "good" stuff; however, I found it had very little flavor (I ordered their "rich" flavor), and what flavor it had was just plain weird. Some people love the stuff though, so it's up to you. Being a newby, though, I suggest you buy either a different juice from their website (I can't vouch for them, not having tried them), or get some juice from a different vendor. If you really want tobacco flavor, try Marlboro or Camel. They don't taste like the cigs they're named after, but they do taste like tobacco. I love my RY4 juice; it's a sweet, caramel-like flavor, but it does have a subtle tobacco undertone to it. It's too sweet for many, but lots of people love it. I buy from myvaporstore.com because they have great prices and very fast shipping.
Anyway, don't worry too much about these things. You're off to a great start with the 510. If you don't like the juice you get, you can always get a different brand or flavor later.