Hi, Unfortunatly I live in the UK and there is no actual brick and mortar vape stores I know of near me, I will be ordering all my upgrades from a UK based online shop. I didn't draw for any longer than I would doing mouth to lung, I just sucked it straight down instead of first holding it in my mouth. Do same length direct to lung use up more juice than standard mouth to lung? I have a lot to learn in this new (to me) vaping world.
Direct to lung with an RDA uses up quite a bit of juice. I can vape all day on my Smok ADC at 3.2 to 3.5 volts and use less than 2ml of juice. I can go through 2ml with my Hobo RDA in twenty? big draws. NOTE: I just tried a long direct lung hit on my ADC. It didn't taste burnt, but it did feel harsh toward the end.
As for no access to a vape shop, I'm in the same boat. As a result, I ended up spending a lot on gear. I've found what works for me, and the rest of my gear I'll set aside or sell (already sold $200 worth on eBay).
So...just trying to save you a few dollars, and unless you WANT to become a "collector", to help keep your gear down to a few pieces that work for you. It's not easy finding the right setup. There's just TOO MUCH information, and too many choices!
My advice is to stay away from the high watts craze. It's not necessary. Your Mini Protank 2 is fine. Buy the airflow base and you'll like it better:
http://www.myvaporstore.com/Kanger-Airflow-Control-2-0-Mini-p/krac-mi.htm
And...what I've concluded about Kanger coils is that they like at least 50%PG juice due to the small wick holes. So, when you buy juice, choose 50/50. If you want to go higher on the VG, shift to the Smok ADC with Micro Core-A coils.
I'm repeating myself here, but I have some RDAs and some 28 gauge Ni200 wire that I wrap around a 3mm screwdriver (RIP Trippers youtube Ni200 build shows you how) and vape with a Hana Modz DNA40 at 420 degrees F at 25 watts. I use a lot of juice and blow some clouds, and I do it safely. I could be doing the same with Kanthal wire and a mechanical mod, but I like temperature control. Nevertheless, IF I had to choose a couple pieces of gear to keep, I would keep my Provari Mini and my Smok GDC (see youtube below) and my Provape-1 and my Smok ADC. I also have some EGO batteries, and I would be happy enough with EGO batteries and my Smok ADC set at 3.2 to 3.4 volts.