Of course you can't fully describe the scenario, or you would already have your answer, but even so, this question seems tantalizingly underspecified. Fix everything, by what standard? Human goals aren't going to sync up exactly with alien goals (or why even call them aliens?), so what form does the aliens' benevolence take? Do they try to help the humans in the way that humans would want to be helped, insofar as that problem has a unique answer? Do they give humanity half the stars, just to be nice? Insofar as there isn't a unique answer to how-humans-would-want-to-be-helped, how can the aliens avoid engaging in what amounts to cultural imperialism---unilaterially choosing what human civilization develops into? So what kind of imperialism do they choose?

How advanced are these aliens? Maybe I'm working off horribly flawed assumptions, but in truth it seems kind of odd for them to have interstellar travel without superintelligence and uploading. (You say you want to write keenly plausible science fiction, so you are going have to do this kind of analysis.) The alien civilization has to be rich and advanced enough to send out a benevolent rescue ship, and yet not develop superintelligence and send out a colonization wave at near-c to eat the stars and prevent astronomical waste. Maybe the rescue ship itself was sent out at near-c and the colonization wave won't catch up for a few decades or centuries? Maybe the rescue ship was sent out, and then the home civilization collapsed or died out?---and the rescue ship can't return or rebuild on its own (not enough fuel or something), so they need some of the Sol system's resources?

Or maybe there's something about the aliens' culture and psychology such that they are capable of developing interstellar travel but not capable of developing superintelligence? I don't think it should be too surprising if the aliens should be congenitally confused, unable to discover certain concepts. (Compare how the hard problem of consciousness just seems impossible; maybe humans happen to be flawed in such a way such that we can never understand qualia.) So the aliens send their rescue ship, share their science and culture (insofar as alien culture can be shared), and eighty years later, the humans build an FAI. Then what?