IIRC, either from BF or Sheldon Brown, a chainline of 50mm is a good starting point. You roughly measure from the centerline of the seat tube out towards the DS of the BB. (if I'm wrong, please correct me!)
Once this is established, you adjust your chainring position, ie. various spindle lengths, dual adjustable cups.

As for cone wrenches, that depends on the hubs since not all hubs are standard hex (lock)nutted. Superbe Pros are machined flats like the cones, Deore hubs are also flats. So, cone wrenches are needed anyway if you plan to re-space your hub. I don't recommend taking a 126-135mm OLD down to 120mm, unless that's the spacing of the frame you plan to use, then it's axle swap time or a hack saw exercise.

Spacers: you can first try swapping the DS and the NDS spacers to see if this brings the hubshell close to your target chainline. Otherwise, one can salvage old hubs for 5 and 10mm NDS spacers. 1mm flat washers will work too.

For a straight edge reference...might try first mounting a well trued and dished wheel on and use the rim edge to rest a straight edge (carpenter's level).
Then measure off it to zero in on your target hub position.