DCC - effect on old Farish loco's

My first posting but I'm sure you guys can help me.

I'm starting a layout after many years absence and reading through this forum and the usual publications it seems obvious to go down the DCC route for a new layout However I have a number of old Poole built Farish loco's that I would like to convert to DCC but I'm not sure what effect DCC will have on these as they were built to either be running or left in an isolated section. They were not built to sit idle in a powered section of track, is it likely to burn out the motor and should I plan to add some isolated sections or do the decoders help protect the motor? Finally I only intend to use two function wired decoders on the loco's (can't see any reason for more functions as I don't plan to use sound), are there any types I should avoid installing on Farish kit.