1. It looks like the p-trap is cast iron??? I'm going to need to move this to accomodate the new shower pan. Should I use cast iron again or go ahead w/ABS? You should use ABS if that's what the rest of the drain is. Also, a shower drain should be 2" pipe. 1-1/2" will work, but the larger size is much more clog resistant and drain fittings don't have to be adapted.
2. How do I get the p-trap out? I only have a 8-9 inch diameter hole to work in(concrete sub-floor). You will need to enlarge the hole, but this shouldn't create a problem with the new shower, it will have to be filled and recovered with concrete. The shower pan should be set in mortar anyway, but this is not to fill that hole, it's to support the base of the shower.
3. If I need to create a bigger hole in the subfloor will this affect my shower pan? The new concrete doesn't have to be thick or "fancy" finished. Just screed it off to basic level and smoothness and call it good.
4. If I need to move the rough in around 3 inches could I do it with a couple of angle pipes? A drain should be kept as straight as possible. You can use some angles, but try to avoid abrupt changes of direction.