iG, P4 and RR is really a great combo to start out with. I wouldn't worry about putting the HD up front (i don't think IDE can go that far anyways). Are you worried about damage caused by vibration or something? A good quality HD will last pretty long in a TC IMO, that is, if you avoid the pot-holes.
I suggest looking into skins for Road Runner that have iGuidance support built in (LSX Void for example). It will save you a ton of time not having to mess with embedding/skinning iG on your own.
Good luck and welcome!