Just want to add my two pence worth to the OP. When dealing with older wheels, it's good practice to drop one or two drops of oil/chain lube or similar into the spoke nipples. Leave a few hours, then turning the nipples will be a lot easier. If you find that the spoke nipples are too tight to start with, back them all off the same amount, a quarter to a half turn. Then bring them up to tension again as you are going through the truing process.
As for spoke tension, without a tension meter and/or experience, it's quite difficult to tell if the spoke tension is in the correct ballpark. There are calculators online where you measure the spoke length and size and it will give you the tension via a musical note. You can then use this musical note to 'pluck' the spokes and get them all up around the same tension. Another way to find out if the tension is off is the first time your ride the wheels. If they feel soft and spongy, you need more tension, if they feel harsh and bumpy and/or if you're breaking spokes, then they're too high a tension.
I'm no master wheelbuilder, but these are my own experiences.