I built my stationary setup using what had been a 7-speed road bike as a dedicated trainer bike and a direct-drive smart trainer. I updated the drivetrain on the bike to 11-speed using a Microshift derailleur and bar-end shifters, although strictly speaking, that wasn't necessary. As it turns out, I do 99% of my riding in erg mode, and for that, I don't need any gears at all--if I had known ahead of time how I'd use it, I would have set it up as a single speed.
+1 to getting the Wahoo Kickr.