The
oil cooler you could probably skip. If your wife is insistent on the heater and defroster, do it now. It does add some heat and if you decide to drive on a cool day she may appreciate it. If you do not put it in now, she might ask for it later and I installed a heater/defroster unit post build on a used ERA that i bought due to NYS inspection regulations and it was a PITA to do once the car was complete.