A1: I use Lightroom Classic as my SPOD regarding all things metadata. And yes, I try to not simply trash DPL’s database on a regular basis because it is, imo, the key to DPL’s way to mature asset and metadata management - and don’t forget that managing assets is not about management per se, but a provision to find things again, be it after some time or by someone else.
A2: With all the care I take, the database gets off track occasionally and then, I either restore the DB from a backup or have DPL re-index the collection, which takes about 30 minutes for 25k images on my Mac.
A3: My focus is on managing my photos and I usually re-develop images when I need or want them. This is probably the opposite of what most people do. I (kind of) push DxO to better DPL’s asset/metadata management because I think that, apart from enabling one’s visions through processing, keeping track of things is as important too.