The key to getting the rim true when relacing it is to make very minor adjustments on the spokes as you go. By minor I mean 1/4 turn of the spoke nipple at a time.
The best way to judge the tension is to tap the spokes with a screwdriver or whatever, and listen to the ring. Compare this ring with that of your other wheel or any known good wheel. It should "ring", not "thud" but not too terribly high of a pitch, just a happy ring.
You will almost certainly not have the spokes all sound identical in pitch. That is okay. That is not as important as having the wheel true.
As others have said, it is "easier" to buy a ready laced wheel. I have found that I don't get a great deal of satisfaction buying things. I would rather repair or rebuild any day.