Don't feel overwhelmed!
It's best to keep things simple at first. This site has people in varying stages of this lifestyle, so you'll be reading technical talk from people that have been doing this a long time.
No need to worry about a lot of that now.
You have, however, made a great determination in looking into liquids to supplement your
vaping. It's really the best thing to do.
While 30ml bottles are always going to be a good bet, it's probably best that you start off with a sample pack or smaller bottles of different flavors. This way, you'll be able to figure out what works for you, instead of being saddled with a big bottle of a juice you don't really care for.
Most vendors will be selling PG or Propylene Glycol juice. It's the standard delivery method. Johnson's Creek has a big selection of the VG or Vegetable Glycerine juice, as well. It's really up to you as to what you like the most. Some people have allergies to PG, so VG becomes a great solution.
It's best, as a new smoker, to try something around 11mg juice or slightly under. That way, you'll be able to gauge your nicotine needs, and adjust them accordingly. After you get that figured out, you'll have a better idea of what to buy in the future.
I hope that's helpful!
Also, as a new vaper, you need to make sure you're ready to purchase additional atomizers and batteries, as the equipment isn't always the most dependable. It's always best to have replacement parts from the start. That way, if you have to send anything back due to failure, you're not going without.