VTA is the slowest of the classes speed wise. But it is by no means the "short bus" class. Many view it as "entry level" due to the speed, but to actually be good at it, take more effort than some of the faster classes. Its less about power and point and shoot driving and more about chassis set-up and driving lines. You have to stay fluid and smooth. One trip to wall-mart during a race and your off the podium. I believe many 17.5 drivers could benifit from running VTA for a bit. One thing is also for sure, driving any onroad class will improve your offroad driving.
As for chassis, I am personally a VBC guy, but a TC4 is a great car as well. Especially if you already have offroad cars with SAE hardware and tools. 99% of all other chassis are metric. But best rule of thumb adbice out there is get something that others are running. It helps with getting a good set-up. I would also recomend a good set-up station. Consitant set-up is critical in any onroad class.
Most importantly... have fun no matter what chassis you get or class you decide to race.