Tesekur for the info, nomadb.
I am riding enduro bikes for years and this time we will be two up on a KTM990. Dirt roads are no problems for us.
Time is, unfortunately, limited

but meanwhile, we stumbled also upon some tips on one part of our trip so maybe you can say if this is OK. On our way to Georgia we plan to visit the Sumela monastery and then continue like following:
Sumela - Yagmurdere - Kayaici - Bayburt - Uzungol - Ikizdere - Rize.
This part should be nice gravel roads with beautyfull nature. As far as i can see from the map, there is no way to do this route in one day so we will maybe skip the part to Ikizdere and head for the coast after Uzungol.
We would be happy if you could let us know about mentioned plateus we could visit. We do not have a fix itinerrary so everything is possible. Thank you also very much for the info about Kastamonu. As we plan to visit Safranbolu, Kastamonu will be on our way so maybe we will find some nice roads in this region also.
On the way back, we will be most probably take the route Kars - Erzurum - Erzincan - Divrigi - Sivas.
On this route, we plan to ride the famous
Kemaliye Tasyolu. Unfortunately, i do not believe that we will have more time after Sivas so it will be only highway to Ankara, up for a drink on the Golden Horn and back home.