The lay down servo trays can be added later but check the compatability between PBS and C-hub (if in doubt just either get them from a PCR or a pro depending what style you go for). the upright ones work fine and are much easier to work around. Tahts one part I wouldn't bother upgrading.
The hyper 8 is redesigned from the ground up but some parts are interchangeable. The steering knuckles and diffs will go on a H7 (c-hub) but not sure about much else (there may be a few other bits I'm not sure).