i did physics, and i dont think you will be at a huge disadvantage not doing physics. Since imo, hsc physics is pree much a rotelearn hsie subject with some calculations here and there, but not too intense overall. Shouldnt stop u from going into eng imo xD
why not combine both uni and business projects? idk. if ur really passionate about the projects and you have a gud team with you and the resources, i reckon u should defer uni and give it a go. But then again there may be other opportunities at uni... who knows?
The optimal approach to paper 2 is to get a good nights sleep, a healthy mcbreakfast and some serious solo contemplations of life after the HSC, "the undiscovered country".