Bearings, a steel pinion, oil shocks, an alloy prop shaft and an alloy motor mount are all good basic items to add to a TT before contemplating any significant power upgrade if you want to keep the car reliable.
Although they look plasticky, the stock dog bones, drive cups and axles are surprisingly resilient. I wouldn't worry about upgrading them until the originals wear out, which shouldn't be for a while yet.
To make the most of your new motor, you might also want to run taller gearing. The "speed tuned" spur gear set is a good start.
Perhaps also give some thought to tyres. The kit tyres are fine for trundling around on the stock motor, but you might find yourself running out of grip when things get quicker. Sorex 32Rs with yellow inserts are a good combo, and are also race legal should you want to visit an organised race event.