It is highly unlikely to get too high spoke tension, in my opinion, at least with modern spokes and rims. In the "olden" times, you could easily potato-chip the wheel with a too high tension or strip the threads from the nipple. One approach is to judge the tension by ear http://www.bikexprt.com/bicycle/tension.htm
. The rim manufacturer can give maximum tensions, but this is only important on lightweight rims (which you do not have). The tension should be quite high, though there is a (in my opinion) wide margin of spoke tension that makes for a strong enough wheel (if you're not dealing with exotic stuff). When the spokes start building up a lot of torsion when tensioning the wheel, you are done (but remove the torsion from the spokes!). Hint: you should lightly lube the spoke threads with some oil. No, this does not weaken the wheel, it only reduces friction in the thread and makes it possible to bring the spokes to the final tension without twisting them too much. Remark: there are cases in which you have to use an adhesive, though, due to manufacturer specs.
The rear wheel has to be dished as much as it needs to be. Sorry, I cannot be more specific, if you want a number. The rim has to sit centered between the lock nuts of the hub. There are dishing gauges available, e.g. by Park, I built mine out of scrap wood.
I can definitely recommend the site http://www.wheelpro.co.uk/spokecalc/
, the available 'book' is quite nice (and inexpensive). I learned wheel building from it (+this site +sheldonbrown.com).