You have the right idea , I also stagger the seal ends & use a small amount of silicone as well , the stagger in the seal will even itself out as the plate is positioned
There is a wire re-enforcement inside the seal so you have to drag the seal virtually all the way around the crank before it comes free
you want to carefully slide the seal around the crank to install it as well , lube it with oil on the way in
the crank may be worn where the angled grooves are but there is really nothing that can be done to repair it
generally yes the flex plate will have oil o it from a rear main seal leak
the side seals are supposed to swell to seal , I generally coat everything with ultra Black silicone though , a billet plate may help it seal better as well