Am I better having Smart TRV's in every room? Some room have 2 rads.
IMHO, yes. That way you can control heating to that room. if you only use the smart thermostat, it will call heating like your old thermostat to all rooms with dumb TRVs. Two, yes, otherwise if any other room is calling for heating, any dumb TRV will get hot too.
Also my Main Thermostat am I better having a Smart TRV in the same room?
You can still have a main thermostat, but as above, without a TRV, any room that calls for heat and the dumb rads get hot. That might be fine for you.