Can't say I need a tank with lots of HP and armour just yet, because I prioritise taking out anything that could hurt the tank, and then either leave it to intercept infantry, or retreat it to deploy elsewhere. They can't kill your tank if you kill off everything capable of doing so first
Either way, the tank is rarely exposed to danger for long. If anything, my main concerns are the big land mines. The small land mines can be safely run over by the tank, but the big ones do a fair bit of damage.
Say, what exactly do you need to do to get the class-specific potentials? I've been grinding Support credits to try and promote my Engineers, but I can't get them to acquire the class potentials too.