New pistons / re-balance?

Are you just changing one piston out?

Also when you do get your stuff balanced make sure you get a printout of all the specs so if you burn up a piston you can order one and re balance the one piston to spec.

As a safety measure it's always good to order 10 pistons so you have extras. But since you say this isn't an all out race engine ordering extra are probably not necessary.

If you have an internal balanced engine evrything needs to be neutral. If you have an external balance you need to have weighted balancer, flywheel/torque convertor.