First NAS -- how to structure storage?

My old WD MyBookLive has been running non-stop for a very long time (more than 10 years) and has given me great service, but 1TB isn't going to cut it these days, so I've upped my game to a Synology DS224+ with 4TB x 2 configuration to start.

My storage and redundancy needs: I'm now retired, so no work-related stuff. All personal. All documents are backed up to Google Drive.

Movies and TV programming take up the most space, about 1TB, but also do not require redundancy. Music and photos (not a pro) require redundancy, the former approaching 200GB (but few additions now) and the latter now at just over 100GB (but I expect continued growth from these). Everything else that requires redundancy is trivial compared to the above.

WIth only two drives, what is the best approach to allocating my (almost) 8TB of storage space? From what I've read, it might also be preferable to use different formatting for these two classes of data -- performance vs. redundancy.

I',m also wondering about the use of an external hard drive connected to the NAS. I have a 500GB drive I've currently got my music files backed up to. How might that fit in with all of the above?

Suggestions greatly appreciated.