Usually I have another set of hands around when doing this. After the steering wheel is straight, pick a common point on the front of the tire and measure across to the same point on the other tire. Do the same thing for the back side of the tire and calculate the difference in lengths to determine toe-in/toe-out and how much.
If you think about it, it doesn't matter if it's the center, edge, or whatever in the tread. It's just important that you measure the same point consistently on the front and back side of the tire.
Bingo!
As far as caster goes, it depends on your steering. For power steering, you're looking for around +4 to +5 degrees of caster. For manual, you'll probably want a little less as lots of positive caster will make the wheel harder to turn. I'd still be looking for +3 though.
With offset bushings you'll probably just want as much as you can get, you probably won't be able to get more than +4 anyway.
For camber I'd be looking around -0.5*, I run -0.75* but that's just me. Usually you can run up to about -1* camber before you really start getting tire wear issues.
Toe should be between 1/16" to 1/8". The goal of running toe in is to actually have 0 toe going down the road. Once in motion, the wheels tend to take up all of the "slop" in your steering linkages- tie rod ends, pitman, idler etc. So, if you set 0 toe you end up with toe out when you're actually moving. If your suspension is all nice and fresh, you can run as little as 1/16" toe in. If its a bit worn, you'll want more like an 1/8" to 3/16".
