Understood, but I've never heard of such a device or software. That’s a somewhat loosely defined set of requirements, which is not something that computers handle well. You’d need something that manages the two connections, monitors your caps, monitors activity, knows about individual users (their needs and habits), etc. That’s a tall order, and about the only thing that comes close is a higher end router (and even then I’m not sure it would quite meet your expectations). If it exists at all, I suspect it would be a business product given the level of specialization ( $$$). Or maybe you could find a software based router w/ these features (WinGate, pfSense, Sonicwall, etc.). But those are pretty complex products and could quickly overwhelm the average user.
That’s sometimes the problem in computing. What seems like such a simple idea is sometimes very hard to implement, or so specialized and/or of limited interest, it’s either never developed, or if it is, it’s too darn expensive.
Anyway, I don’t mean to sound overly pessimistic, just realistic. If I think of something over the next few days (sometimes you have a brainstorm late at night), I’ll report back. And hey, you never know if the next guy has discovered something wonderful and just right over the next hill.