The markings are irrelevant. They serve no purpose. They're supposed to measure the amount of liquid, but it is totally incorrect to a point where it is laughable. So don't count on that as being a single sign of low quality. That's not to say I'm not guaranteeing they're high quality--GotVapes probably has the ultimate top notch of those.
It all depends on your budget on what you order from where. Pretty much every vendor does a flat rate ~5-6 box. So each person you get products for adds that much. At the same time, you want to get quality products. I got my stardusts from litecigs, only because gotvapes sells out of them within hours of restocks. But, I got other cartomizers and juice from gotvapes. However, I get most of my juice from freedomsmokeusa.
So every time I make a big order, I usually spend from 10-15 on shipping alone. But I try to buy a lot to make it worthwhile--I'll buy 200mL of liquid from one place and 5-10 packs of cartos and a spare battery from another place.
I would get some high nic juice and some medium. High nic (18+) for early morning after meals and high stress, medium (11-16) for standard cravings, but if 16 was doing if for you, then stick with it. I did 36 mg for the longest time, but I smoked roll your owns with no filters but also was at 5-8 cigs a day. It varies person to person. I have an extremely high nicotine tolerance. I'm relatively sure I could vape 50 mg and still be fine.
Filler cartos (boge/smoktech) and CE-2 (clearomizers/fluxomizers) are both very popular. Both have a different feel to them and it's a matter of testing them out. Stardusts are a variation of the CE-2 system. LR (low resistance) and dual coil cartos are the "new thing" in filler cartomizers.
