Use three bases and accept one return through Tbilisi
Spend two full days in Tbilisi, two nights in Stepantsminda, return to Tbilisi for a practical night and finish in Kutaisi. The return may look repetitive, but it protects the mountain plan and places you near the westbound departure.
Check the Georgian Military Highway before leaving. A direct minibus and a driver with sightseeing stops are different products. Keep the first Stepantsminda afternoon light and choose the full-day walk from the forecast and local advice.
Make Kutaisi a city stop, not an airport label
Identify the exact westbound train or road arrival. Kutaisi I, Rioni and the airport are separate. Use the final day for the centre or one carefully arranged heritage visit only if it leaves enough time for departure.
Keep the same Tbilisi room, or arrange reliable luggage storage, for the night between Stepantsminda and Kutaisi. This makes the repeated capital stop useful rather than wasteful. In Kutaisi, choose a central room unless an early flight genuinely makes an airport property more practical.
With six days, remove Kutaisi and return to Tbilisi. With five, keep Tbilisi and Stepantsminda only. Do not shorten by attaching a flight to the normal mountain-road arrival.