Vegetation becomes more important as competition to algae, help with plant - nutrient - productivity balance, and some habitat for fish. Goals for the pond are important for helping to determine the amount of beneficial vegetation. Since your pond is in a valley it will get lots of leaf and outside organic inputs into the dammed up water flow. Annual flushing and short turnover time will help some with reducing overall nutrient accumulation. Organics will tend to settle and accumulate in the pond basin. Generally IMO all plant problems occur in shallow water so the less shallow water the fewer the plant problems that will occur especially long term.
Nature will introduce naturalized plants; some good,,, some not so good. Do some reading and home work in this link. Steep sides will help minimize submerged vegetation that usually promotes clearer water as submerged vegetation competes with plankton and submerged algae. If it were mine I would introduce some of the beneficial plants discussed in the link.
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=440475#Post440475
