FBinNY 

Part of the problem is that you're trying to build a house without a decent foundation.

Here's some critical info that may help.

1 the rim's location is determined by the spokes' lengths (hub to nipple), not their tension.
2 spoke length changes rim position differently radially vs. wobble. ------ Every full turn of the nipple moves the rim about 0.5mm radially, and about 8-10mm sideways.
3 early on, there are low strength variables, mainly related to the elbows that can seem significant at low spoke tensions, yet are nearly insignificant compared to final tensions.

So, focusing on length, trying to be accurate to within 1 full turn will produce a wheel with radial true within LT 1mm UNLESS, you muck it up by "correcting" the false errors that appear early on.

Short version --- use good process and TRUST it to produce good results. Fine tune only near the end.