RE: Best way to attach horizontal stab straight?
Actually, there are about as many ways to do this as builders. You just need something to hold everything in place as you get them aligned.
We'll assume that the components; fuselage, wing, stabilizer, and vertical fin are all build straight and true.
A cradle to hold the wing dead-level is a must. Then align the fuselage to the wing. Check, check, check. Then clamp it in place and put in your hold-downs. Now align the horizontal stabilizer to the wing and fuselage. Use long sticks, string, a level, a square....whatever you need to get it right. Glue it into place. Do the same with the vertical fin.
You can do these in any order. If you have straight components, then careful measuring and alignment will always give you a true model.
We prefer to do the wing first, and then the tail. We find it easier to block the wing at its suggested incidence angle and then adjust the stabilizer to the proper relationship.