Sure.

But like I said, I'm coming off years of single chainring gearing, and the issues feel like news to me.

Speaking to chain suck, I believe it has to do -- for my case of new rings and relatively fresh chain, at least -- it seems to happen when I shift both front and back in close succession; I think it has to do with taking off tension from the rear D at the same time as shifting the front: the chain can easily be carried along the chainring with the front shift if the rear gets slacked by a poorly (read: simultaneous) timed rear shift.

That being said, the chainrings which have occasioned me to experiment this phenomenon are only as old as the first cassette which I've run through them, so I'm wary to account their behavior to wear, rather than poor use.

Speaking to the other issues you mention (ie. poor shifting, un-smooth riding, and 'looks like shift' (? -- never seen that one ): I don't much want to wait for my shifting to deteriorate beyond repair without my having replacement parts on hand, but seeing as how I don't quite know what to expect and I don't have spares in stock, I am hoping for an expert guess-timation at what I should be planning for.

Frankly, TLDR: would a rule of 3 kind of thing be conceivable (3 chains to a cassette, 3 cassettes to a chainring-set)?

Or does that strike you as way too few cassettes? Given that I'm not planning on using this information for scheduling replacements -- I will be taking that decision on an 'as needed' basis -- but rather on gleaming a vision of what may be to come for the chainrings, and possibly ordering prophylactic replacements sooner rather than later, depending on the consensus.