Most people consume 3 - 5 ml of juice a day. Most juices will come in a 50/50 pg/vg ratio. Most of the custom juice vendors allow you to choose either more or less of the pg or vg as well as the strength of nicotine. Some will even offer a choice in the flavor strength.
I also recommend ordering sampler packs from new juice vendors if they offer that. This can save you money in the long run in case you don't like a particular flavor and then have a 30ml bottle of juice you may never use again. Once you find a sample flavor that you like, you can order more in a larger size.
Finding a couple of juice flavors that you enjoy is probably as important as finding the right gear setup. It's hard for experienced vapors to recommend a flavor or a vendor as taste in juice preference is extremely subjective. Just be aware to not chase the idea of trying to find an e-liquid flavor that will taste like your cigarette. It can't be done. It's impossible to re-create the taste of burning tobacco and smoke. And once you have quit smoking, you'll realize you don't want to vape that flavor anyway. Believe it or not, vaping can be more enjoyable than smoking ever was.
I have found that I personally prefer juice vendors that use all-natural, all-organic flavorings. They just taste more flavorful and accurate, never having an artifical taste to them. The below vendors sell these:
https://natural-eliquid.com/store/index.php
Organically Flavored E-liquid | Virgin Vapor | Electronic Cigarette Organic e-Liquid | Electronic Cigarettes
Organic Flavored Juices