First, wires crossed somehow and I missed the piece about having a 10 speed derailleur. I was thinking 6 speed for some reason. So now agree with Harry regarding the need for a cartridge type drive. I stand corrected! Apologies for any confusion created.....
On the direct drive vs. geared hub, I had a couple of direct drives before learning how gutless they are as compared to a geared hub - for my purposes. Remember I'm 300lbs. Like Harry mentioned, I've played with both a 750w, and a 1500w direct drives (on the same bike). They were both replaced by the 1000w MAC geared hub motor, which just annihilated the direct drives from a performance perspective, AND did that while extending the battery's range from 25-30 miles with the direct drives, to an easy 35 miles with the MAC. I literally removed the 1500w direct drive, and installed the MAC with no other changes. Same controller, same everything, so it was a heads up, everything else equal comparison.
Regen - I can help a bit there I think. I messed with that quite a bit too. Using the 1500w direct drive motor and KT controller, in an area that has some pretty big hills to try it out/play with it in. Frankly, I wasn't impressed. At speeds of say 15mph and climbing, you could engage the regen and at best it would attempt to keep you from gaining much speed as quickly as you would without it. That's it. There's no drama here! As far as replacing power used while you are coasting or going down a big hill, that's just not going to happen. At the very best, you can say it may have put some power back on a really long hill, but I doubt seriously you'll ever be able to measure how much. For all practical purposes, regen is about braking power on big hills at speeds over 15-20 mph, that's it. If anyone tells you differently, they've never used it. They've likely been reading some sales hype somewhere that's complete B.S.
In all but one case, regen is not available on gear driven hubs. The one geared hub that does have regen is a whole different class of motor from Grin. It's based on the MAC motor, so it's very high quality, and it's not cheap. There's a LOT to that (from how that's possible mechanically to the electronics involved), so I'm not going to go into that here. You can read (and reread several times) that info at Grin's web site. As mentioned, there's a LOT to that....
The KT display has a place where it can display motor temp, but I've seen no way to feed it a signal from the motor up through the controller. I've never seen any detail that would allow that either, and I've done maybe 10 of these KT installs dating back to 2015 or so, to the most recent ones done in the last few months. If somebody knows how that might be done (feed the display temp data) I'm all ears! Don't forget, the motor will need that ability as well. I don't think the Bafang geared hubs come that way. FWIW, the Bafang mid drives take care of that for you. If they sense the windings are getting hot, they'll start tapering the power to cool them.... -Al