There will probably soon be a better reply than this, but here goes...
These planes all came with rigging instructions. The Bristol F2B Datafile has some of this for the F2B reprinted in the back of that book. Dihedral, incidence and trim all had factory settings. Something called an Abney Level was used to check the angular settings, and measurements from a known or obtainable straight line checked "squareness". A few aircraft (SE5a, Snipe, 1 1/2 Strutter come to mind) had in-flight adjustable horizontal tail planes, so pitch could be trimmed to level flight. As speed increases more lift is generated, causing the nose to rise, and as speed decreases the nose would drop. Somewhere in the middle is a neutral point, giving level flight with zero trim on the tail. Roll and yaw had to be adjusted as you described: trial and error until it was right. I would guess that properly adjusted pitch, roll, and yaw in a properly built airframe in good repair would fly level. Back or forward pressure on the stick, depending on speed, would be necessary on most aircraft without adjustable tail planes.