For speed and quality, I've had great luck with the fujitsu scansnap. Mine is much older. I'm not sure what types of improvements they've made (or have ruined). It was great for batch photos and documents. I have no experience with how it would do with slides or negatives, but for pictures, I think it was good.

1. Roll your own budget NAS
2. Find the cheapest dollar per terabyte storage you can
3. Profit

I think you'll probably be installing something like plex on a custom built or a synology.

It's more of a question of how much time you have and budget. Do you want something with nextcloud like functionality out of the box? Synology isn't a bad choice. It has all the apps for cloud backups, quotas, users, etc.

Do you want to toy with your system more? Roll your own and choose the best software for your needs.