Same, except I also use Scrutiny to flag drives for my attention. It makes educated guesses for a pass/fail mark, using analysis of vendor-specific interpretations of SMART values, matched against the failure thresholds from the BackBlaze survey. It can tell you things like "the current value for the Command Timeout attribute for this drive falls into the 1-10% bracket of probability of failure according to BackBlaze".
It helps me to plan ahead. If for example I have 3 drives that Scrutiny says "smell funny" it would be nice if I had 2-3 spares on hand rather than just 1. Or if two of those drives happen to be together in a 2-pair mirror perhaps I can swap one somewhere else.
What does "mediaserver" mean to you? Synology are good for storage but not so great for more CPU intensive stuff, plus of course they're not freely upgradeable and you're tied to their OS.
If you're comfortable building your own PC you can install Unraid or TrueNAS which will give you an easy to use admin interface and the ability to use/upgrade with off-the-shelf components. /r/buildapc can probably help with that.
If you're also comfortable with Linux you can design your own fine-grained approach to the OS and the apps on it, /r/selfhosted can probably help with that.
SSD's are getting there in $$$/TB but have a bit more to go to catch up to HDDs.
Your approach of having multiple backup drives is sound. Having everything in one place means all eggs in one basket. Keep that in mind when you reorganize your data.