I think the FT kit comes with a 72 (?) teeth, 48 pitch spur. I would stick with that while you're getting started, but if you want a quieter car go with 64 pitch. 64 pitch is finer and will give you more gearing options, however it is not as durable, meaning you will have to pay careful attention to setting the pinion/spur mesh. 64 pitch is much quieter, but if you are going to be running the car in anything less than very clean conditions I would not recommend it.
As far as a 64 pitch spur, I believe I have a 100 tooth in my car, which is a nice even number and about as large as you can get with a TC3. I have no idea about gear ratios for a brushless motor, so someone else will have to give you some advice on what size pinions to buy. Brands to look at would be Robinson Racing, KW spurs (dist. by Shumacher USA), and Titanium Racing.