Hi Melissa,
I'm not sure exactly what kind of sinus surgery you'd be having, but I did have surgery when I was a freshman in high school to remove polyps from my sinuses. I had many sinus infections growing up, and I think the point of removing the polyps was to stop the infections from recurring. Anyway, all they did was go up through my nose and clear out the sinus cavities below my eyes; they went up the ones to the forehead as far as they could reach as well. In the 12 or 13 years since the "clean out," I've had only one sinus infection, so I think it worked.
From what I can remember, I was in the hospital overnight but I didn't really feel that bad. The worst part was when they pulled out the packing from my nose and blood started gushing out (sorry, that was kind of graphic). I would say that the sinus surgery was much "bloodier" than the AN surgery. But I think you should definitely get it taken care of. Oh yeah, I couldn't drink out of a straw or play my clarinet in band for two weeks after because they didn't want the pressure to disturb any of the healing going on inside. I would imagine that if you did this soon, it wouldn't interfere with BAHA surgery in June.
Hope that helps!
Kim