VrayCamera\PhysSky\Background Help (tips) Please

Is it correct that if I use a VRay camera with exposure I cannot have a background other that the VraySky or an HDRI with its multiplier turned way up?

Can I use VraySun\VrayCam (with Exposure) and replace the background?

How can I get sky reflections with the background off? (HDRI,Vraysun and bitmap?)

Thanks. Getting this clear would be great!

PS-Which does everyone prefer HDRI, VraySunSky or a combination (if there is such a thing)?

Thanks again!!

-T