There was a time I used my TC for TM and storage. The TC is essentially a shared disk and TM backups are just plain accessible directories showing up in your finder, the same way as they would show up on a normal USB drive with TM activated on it. However TCs are not very known for breaking speed records. I have since switched to iCloud storage and use the TM only as wifi access point.
For the storage part I used both normal storage and a couple sparse images I created in Disk Utitlity. One for iTunes, one for Photos, etc.
While the iTunes disk is quite forgiving when starting up without mounting the image first (iTunes will complain it couldn't find the last known library and give you an option to fix it), Photos.app is not.
Chances are you're not always connected to your home network and, when you're back, chances are your Mac won't see the TC right away after connecting to your Wifi. Photos.app eventually will catch up automatically, but not without giving you random punishes along the line.
Photos.app gives you the option to store lower resolution pics on your iOS devices, but stores full resolution pics on the Mac.
Yes indeed there is an option that says "Optimize Mac Storage" but the fineprint under it says "Store full-resolution photos and videos in iCloud. Originals will also be stored on this Mac if you have enough storage". Apple understands that people have multiple iOS devices. They don't see to understand others also have multiple Macs.
Bottom line: If you're up for a frustrating ride, store your photos on your TC - in either way (direct of sparse images). Using external USB3.0 drives instead is not ideal either, but at least it will save you a lot of time.