So we once refurbished old doors and would never do it again. After 3 doors we gave up, the 5th just stayed as it was and the 6th we bought new instead and altered the opening in the masonry to fit the standard size. The door was from the hardware store, was installed in 1-2 hours and cost maybe 150-200€ (it still works very well, it is now about 6 years old). The old doors... don’t get me started. They had been painted numerous times. You couldn’t sand off the paint because the paint would ruin the sandpaper in no time. On top of that, the doors had many details and even glass inserts. Removing the paint with heat and a spatula was a job of... no idea, several days per door, my husband was cursing a lot and could hardly move his hands afterwards. Then sanded, repainted, and in the end you still had an old door. Sure, they were detailed solid wood doors, but our restoration simply wasn’t 100% mastered, so it just didn’t look 100% “successful.”
We are currently in the process of buying an old building. We will install cheap doors ourselves (that’s not rocket science). We also have 2 small children who unfortunately are not gentle. That’s why better something cheap that the kids can draw on, bump into, etc. The doors are beyond saving if you don’t want to invest a disproportionate amount of time, so now new ones and also brought back to standard size. But really too ugly and worn-out and messed up to just “leave in.”
Bringing old to new shine is always great. But often it takes a very long time and in the end maybe doesn’t look like you want if you have no experience. You definitely have to consider it individually. Whatever you decide: I wish you good success!