Right now the wallet in Bitcoin Core is disabled if pruning is enable, so I don't think that will work
It is my understanding that removing this restriction is a high priority task item for the Bitcoin Core developers. I don't exactly follow their progress, but many people expressed interest in having both pruning and wallet working at the same time.
I should've quoted this portion of your original message in my reply.
3) A third way would be to open the UTXO BerkeleyDB database file (can this be done while Bitcoin Core is running?) and then check if our addresses match.
Yes, this can be done for BerkeleyDB but not for LevelDB. Apparently there exist code that is LevelDB-compatible and fully multiuser/multitasking but it is only available from Google for money and NDA.