Synology's NAS Selector is Underwhelming - So I'm Looking for Setup Advice

I feel like I see a lot of people ask advice on what NAS will fit their needs. Synology isn't alone but really wish they would invest in some AI assistant to tailor suggested products to the user.

A little background on my setup:

• Whole house has dedicated Cat6+ wiring
• Unifi setup; UDM-Pro, Switch, WiFi APs, half a dozen POE Cameras etc.
• Most devices (e.g. TVs, PCs, Cameras) are hard wired into the router

What I'm looking for:

• Want to reduce dependency on cloud services for data backup and access my data from anywhere like I currently do on Dropbox/Google
• Integration with PLEX or something similar to stream Blu-ray/4K+ to TVs/PCs
• Extend NVR capacity as UDM-Pro only has 1 bay
• Rackmount form factor