As you are probably aware, STP is a layer 2 protocol. Router is a layer 3 device but router interfaces can also be configured as layer 2 ports, using bridge-group command, in that case you can enable STP in a router and it functions the same way in the router.
Agree with the previous poster. Naturally, when you add more processes it's going to require more CPU cycles but with the powerful processing capacity of the newer routers that shouldn't be a big problem. If you can then keep bridging separate from routing functions. However, if you have to bridge/route traffic from this router then that shouldn't be a problem.