It's been a few years since I read through the ownCloud manual, as I switched to NextCloud after the mass exodus of ownCloud maintainers back in 2015ish to form NextCloud. I ended up going with Nginx, but if IIRC there's a section in the ownCloud manual about Apache.
If you haven't thoroughly read the manual, or haven't had prior experience with Apache, it would be recommended to configure a VPN or tunnel access to owCloud over SSH, as you don't want to expose it's webserver to WAN unless you're 100% it's secure and is not exploitable. If you do choose to leave it directly exposed to WAN, it definitely needs to be in it's own vLAN with no other devices and strict firewalling in place for it's vLAN.
- I have NextCloud running in a FreeBSD jail, and I'm not sure what your underlying OS is on the Pi, but, if possible, you definitely want to jail it to protect the underlying OS.