What you're really asking about is dressing and sauce. The crown roast itself is fairly constant. From a technique standpoint, it's very likely the dressing will be relatively easy. While you can go nuts making a complicated sauce, considering the nature of the party (one you attend as well as cook for), it's probably best to keep the sauce relatively simple and as much make-ahead as possible.
There are any number of possibilities, including Chef Petal's suggestions of course.
Is there some preferred direction in which you'd like to go? Sausage dressing? Figs and fruit? Apples? You name it. Not a problem.
Brining can be a bit problematic on pieces of pork that size (bone-in loins) -- not that it can't be done, but the timing can be a bit tricky. Injecting is another possibility you might want to think about. It's not much help, but if it were my crown roast I could go either way.
I'd definitely think about smoking the roast for a little while, then moving it indoors to finish cooking.
If you don't wrap the bones with foil, they'll char during the cook. I think though, that modern and best presentation is to allow for that. Creamy-white bones with frilly "panties," are a bit fussy and old-school. But, it's your call not mine. One way or the other, it's something to plan. Speaking of which, after the bones are frenched (whether it's by you or your butcher), you'll want to burnish them with the edge of a metal or the back of a knife -- to make sure they're absolutely clean.
Let us know how your thinking progresses. If you want a completely written out recipe for roast, dressing and/or sauce, knowing what you want would make a big difference.