welp. that's a bunch of questions. hahaha I have a K2, owned a K3 for a couple of years, and the wife has a K7, all 1000's. I have ridden my bud's RT(yea, he loves me) and I recently rode a K13 wee(650) adventure..here's my thoughts:
first off, the adventure model seems like a base model with some overpriced accessories you can get aftermarket. nothing really special, I'd suggest maybe saving some cash and buying better stuff aftermarket.
The 650 I rode was not underpowered in any way, and was a fair amount smoother in power delivery and overall vibration. Being that you're planning to spend a lot of time in squirrelly situations(off road, gravel) I would think the light weight would be an advantage. If I was riding single all the time, I'd prolly switch to the glee - meaning the new 650. Hell, I may switch anyway once the K2 is worn out. The 1k has a lot of additional torque(perceived, anyways) in the lower range, but I don't know that in practicality it's that much of a difference.
To my knowledge they're exactly the same chassis/seat/peg/bars config, so comfort is same. The ability to stand on the pegs is a huge plus, add highway pegs for additional position. It's going to be lighter than your RT, not quite as solid on the freeway, but certainly fine and tracks well. It feels solid, in other words.
There's a lot of surface area on the front of these things, so it's going to buffet more than your RT. Lowering the triple tree/raising the fork tubes a little bit seems to help, as well as sharpening the handling a bit.
I dunno, just my thoughts as a long time V owner. Of course, I'm biased.