[tdq]

I have a NRP 12 fret black rust, single cone steel reso. I love it to bits, I do prefer playing it sitting down (but I like to play all my guitar sitting, even electric, if I can). Having said that I have played it standing up, and although definitely heavier than a regular acoustic or electric, I didn't have that much problem with it.
As for single-vs-tricone, and wood-vs-steel, I find that the steel/wood makes a bigger difference than single/tric, although of course that is there too.
(I have never owned any of these, this is just from trying in stores)
I did try a wooden M14-T Thunderbox and it was fantastic - loud and such a beautiful rich tone to my ears.
What would I have done differently? I still would have gone for a single cone, probably still 12 fret, but I could have wavered on the steel/wood. Steel is brasher and livelier but the wood tone is so dang nice.