Im sure more people will come soon and answer this better but ill try to answer some.
Dna is the name of the chip that regulates things its made by a company called evolve. they sell the chips to the mod makers.
40w is the highest they do for now as they want to bring good and new features rather than play the high power race. They were the first to do the temp control.
The temp control sounds handy but only works with nickel. (and titanium i think) You can use regular kanthal but the temp control bit wont work.
You could try and limit your temp by using less watts but setting a temp is more accurate. I read you can tweak your temp to get better or slightly different taste from your liquid and i think if you get it right keep it below your wick burning temp. I havnt used one but another benefit i guess would be keep the watts high so the coil heats up quick but then the temp control would keep it feeling like a lower setting.
Looking via google the ohm limit is 0.16 - 2.0.
They are expensive but they are generally thought of as one of the best chips, there are many clones now that do work but have been known to not last as long or not work quite so well. The other chips that i have read as working well is the YiHi chips. ( hope i spelt that right)
I would love a DNA my self but I'm not that rich at the moment.
Something like this. (no idea if this site is any good just was top on google.)
http://www.vapinart.com/cart/Vapor-Flask-Dna-40-Black-P1444.aspx