@gyrex, The difference between the iStick with the Nautilus and the Kanger Subbox kit is pretty much 2 issues. The Nautilus is more for mouth to lung vape then the straight lung hitter. The Subtanks are more for the lung hits. I use both every day, but I still mouth to lung. When I got my subtank the first thing I did was to replace the wide bore drip tip with a regular sized small opening cheap drip tip. I also use my subtank on the single hole opening. With Subtanks you're going to vape more e juice (so DIY is the way to consider when you get to this point), which in turn consumes more nicotine and then you have to lower your nic level in the juice. Most sub tank users vape at 6mg or less.
With the subtanks you need to understand how ohms law works and then the coil building stuff (I recoil my stock factory OCC's, it's not really that difficult). The Subbox is nice and I considered getting one until I found out it doesn't have a spring loaded 510 pin. (the pin in the battery where it makes a connection to the tank). Having a spring loaded 510 pin (like the iStick 30 W, and the new iStick 40 TC (temp control)) allows the user to use various tanks without concern, as some people have had issues damaging the 510 connection.
Temp control is the next big thing. Lots of manufacturers are coming out with TC. Basically it is a safety issue that stops the coil from firing when it gets to temps outside the safe range and give you a dry hit. You have a lot of decisions to make and I wish you luck in your vape journey.