You do not need to drive to enjoy Kazbegi. Stay in Stepantsminda, use local 4x4 drivers for Gergeti or longer valleys, and keep at least one day flexible for weather.
A simple two-night setup
Use arrival day for the town and the church if visibility is good. Keep the second morning for a walk or a locally arranged 4x4 trip to a valley such as Juta, subject to current access. Ask your accommodation which routes are open before leaving.
Why local transport helps
Mountain roads and trail conditions are not always obvious from a map. A local driver can tell you whether a route is sensible that day. Confirm the price, vehicle, waiting time and return plan before setting off.
Pack for changing conditions
Bring layers, water and shoes with grip. The town can feel mild while the ridge is cold and windy. Do not plan a long exposed walk as your only activity.