How do I go about...

-Determing exactly what Bore piston I should buy? Is it safe to say that a low mileage ZC is going to need the stock 75mm bore?

I never build a motor without boring, always trues everything up so you know everything will be perfect and straight. Bore .25 or .5mm

-Determining what size berrring's I need. Do I use the old berring's with my new Crower's and do the whole plastigauge thingy?

Always plastigauge, use whatever main bearings come out of the motor and use the numbers on your crank and Crower's recommendation to size bearings for the rods, but always plastigauge afterwards.

-How do I tell if a Water pump need's replacing(with out running the motor)
-" same question "....Oil pump.

Always replace the water pump on a rebuild, they're to cheap not to. Oil pump is iffy, I've never seen one fail, but if it has over 100k and this motor will be subjected to lots of torture, bite the bullet and buy one.

-Do I need to replace the Crank Thrust berring's?

Only if this was a 5speed car. Automatics won't wear the thrust bearings.

I feel confident in most of the awnser's to those question's, but I just want to make sure, and also get some opinion's/experiences.

Cause, ya-know this isn't somthing I want to F*CK UP!!

Thank's for any help