On my Ras Pi 3, I am running Openhabian, with Openhab2 and Pi-hole running fine, w/ CPU load usually 1-2%, sometimes going up to 10%.
TVHeadend would likely be much more intensive. Do you think it is a bad idea to run it on the same Openhabian installation on the Pi? My OH2 does not run critical components – mainly speakers at this point.
It isn’t CPU you have to worry about but RAM. OH is likely taking up half a gig of RAM on its own. I don’t know about Pi-Hole but if TVHeadend takes a lot of RAM it may not work.