Hello,
Many thanks for your positive feedback!
Orthanc can only use its own, embedded SQLite database engine. However, Orthanc can transparently work in parallel with MySQL, within a LAMP server: You do not have to setup anything particular, as SQLite does not require any database setup. You just have to specify in the Orthanc configuration file where to store the SQLite database.
Regarding Apache, Orthanc can be setup behind Apache using the "reverse proxy" mechanism:
As a summary, even if Orthanc uses Mongoose/SQLite, nothing prevents its use on a standard Apache/MySQL box.
HTH,
Sébastien-