The highest stress points of the rocket will be the engines. If I were to guess (which is all anyone can do), the booster can be re-used a practically indefinit

The highest stress points of the rocket will be the engines. If I were to guess (which is all anyone can do), the booster can be re-used a practically indefinite number of times (>100 launches) - while the engines need to be replaced every K launches on average. They might be able to stretch engine lifetime if they are good enough at shutting the engine down on failure. If they can tolerate one flaky engine on a launch, then they can blend new engines with old engines to improve re-usability by running engines to failure. Question is how good they are at shutting down the engine as catastrophic failure could take out the whole vehicle. Space Shuttle main engines could be re-used 3x on hydrogen/oxygen fuel, and those maintenance schedules were set in the 80s.