Hi Ali,
The auto paint feature will stop if you click in the picture. There should be no problem saving it and later re-opening it to work on it more. I use it on a PC, not a Mac so maybe someone else uses a Mac and can offer advice. Jenifer might help on a specific question but you should provide more detail like are you saving in the RIFF format.
The restore detail brush (soft and hard) clones image detail from the original to the painting. If you save in a format that does not keep layers, that will go away when you re-open. I usually save in RIFF and Jpeg. If I'm happy with the final result, I keep the Jpeg and delete the Riff knowing I'm finished with that one. Others may keep Riff format. Welcome to the group.