1, Balancing is always a good idea. Wont make much difference to performance.... But will stop accelerated wear and give the engine a much longer lifespan! 2, All the tolerance should be checked to make sure there to spec yes! 3, Valves and springs are not somthing that generally needs doing... Stem seals would be a wise move as would re-grinding in the valves and de-coking them tho! 4, 74mm is standard. Its always wise to go up to 74.5mm to get a nice fresh surface for the new pistons and rings to bed into! Hope this helps!