Since you're using Ubuntu you can probably sign up for Ubuntu Pro, free for personal use last I checked. This provides you with additional security updates. (I would suggest using the LTS branch)
Look into hardening your os and apache installation. Such as using certificate based authentication exclusively for SSH.
Put this box on a separate network (such as a DMZ).
Create regular backups and do recovery drills to insure it's working as expected.
Generally speaking it depends on how you're transforming the work.
I suspect incidental use like in a short parody could be ok. But let's say you stole Misty's voice from Pokemon and tried to make your own free web show with it. You'll probably be in violation of fair use clauses.
This is all heavily dependent on jurisdiction and this is not legal advice.
That's my life currently 😂😭