Vertical motor mount, 19T pullies and alloy spur holders are what I would consider mandatory. Titanium turnbuckles when you get tired of the stock ones having round rings instead of machined in hexes/squares for adjustments. Same with the alloy shocks -- the clip on adjusters get old. Everything else you can add if/when you have an issue or break something or just feel the need for CF/alloy.
I've got 3 Zero chassis and 2 Mini chassis that I use 3Racing shocks on. Counting in my head I think I've got 28 3Racing shocks currently on chassis or ready to go with alternate springs/oil and I've sold off some of the plastic bodied ones. I've never had an issue with any of them leaking. Other than the color of the alloy I think the Mini shocks are identical to the Zero shocks. Build them carefully and make sure all the plastic parts are "clean" and don't have any burs or sprue remains. Make sure that you don't damage the o-ring when sliding the threaded portion of the shock shaft through it. I normally assemble the bottom portion of the shock body and then the top portion of the shaft. Put a couple of drops of shock oil into the body and then slide the shaft through. That way it's coated with the oil when it slides through the o-ring and the bottom of the shock body helps keep things aligned so threads have the least chance of damaging the o-ring.