New pistons / re-balance?

Not sure I understand why, but if this is a NEED and not a WANT then I will be on my way to the balance shop before this gets buttoned up.

What parts other than the internal reciprocating/rotating parts do I take to them?

Does this mean that the motor needs to be intenally balanced?

Can the motor be balanced and still use an external balancer?

If both are an option whats the difference both performance and cost?

Please help continue to straiten me out here. Still soaking all this in.