rfun6 - The batteries link you have would work in the Chuck (but not the Little Chuck). Those would run at 3.7v (actually when first charged, more like 4.2v I believe). You would use 2 of the 3.0v CR123 little batteries in it to run at 6v.
Here is a review of the Chuck at 6v
http://www.e-cigarette-forum.com/forum/electronic-cigarette-reviews/38540-chuck-6v-review.html
I decided I didn't want to worry about blowing attys, so I run both of mine at 3.7v and they pump out the vapor with my 801/302/RN7042. I'll probably buy an adapter soon so I can run my 510 on it as well.
The Little Chuck is 3.7v and has about a 7 or 8 hour run time on the battery that fits it (16340).
For either battery, the mAh is the length of time it runs... the higher the mAh, the longer it will last.
No LED in the works that I know of. I find the button perfect. It is really small, but presses with a nice easy pressure (but won't just discharge by a slight press against something else). I usually have it in the crook of my finger to work it, and it is quite comfy there. I don't know if Jeff has plans to change it, you could ask but so far even big handed guys haven't griped about the button.