I've finally pulled out my TF Zero kit from under the bed and will be building it this winter.
Any suggestion or recommendations from anyone whose built this kit before?

Put 80 flights on one this year. Mine is powered by a OS 1.2 4cycle, with Spring Air retracts, and flaps. Mine started with a K&B .65, Reliability forced me to my old stand by Super Tigre S-61. It flew fine with the S-61 (it flew on the wing) but on landings I did not have enought prop past the cowl to make an affect once I was flaired and adding throttle to lighten the touch down. I had a 1.2 on the shelf so I put that in it and it was perfict all those bounced landing were gone. AT-6's have a tendency to bounce on landings if not wheel landed but with the OS 1.2 $ cycle that has been saverly reduced.
In the kit they give you landing gear mounting blocks that are made of marine ply. I epoxied them in but in these bouncing fits it would have (on the occation when I screwed up a landing) the mounts would break out. The epoxy bond would hold the glue joint between the layers of ply would fail. I ended up putting maple in its place and that has held up great.
The firewall is all Lt ply. Re-cut those peaces out of marine ply if you plan to put a big engine in it. Fiberglass cowl is a must, the plastic one will start to crack appart after about 20 flights
With the OS 1.2 4 cycle and flaps at 8.5# my flight envelope is 110-93-25mph, that is about 110 mph in a full power dive ( not recommended), 93 mph top speed level, and a dirty stall speed of 25mph. All but the level speeds are estimates, the level speed was checked by the local constable.

paladin, is the cowl for the Zero large enough to completely house the OS 120 4 cycle engine?

OS Max 1.2 4cycle the rocker arm covers stick out. Mine is sidw mounted.

A .60 2cycle (My .Super Tigre S-61 was one with the old machined round head, purchased 1978) can be totaly enclosed but I had over heating problems till I cut cheeter holes.