Raspberry pi 3 both Gateway and Controller
is it possible to make my pi3 a gateway for the sensors and also run a controller, all in the same board?
Yes it is possible. I have the NRF24L01+ attached directly to a pi3, with the mysensors gateway and MyController working on the one device. I added a RTC as well and have a neat and compact solution that wasn't possibe even a few years ago!