Hmmm…. “Wildflower Seeds”<=>“Just Weeds” Especially when not blooming, those two bear a strong resemblance to each other! Nevertheless, you asked about shrubs and trees to make the slope more attractive, and since Mother Nature will be their only moisture, natives are definitely the way to go!
Mr Smarty Plants recommendations often come out of the recommended species lists. This one is for New York. At this point one could limit the search to “shrubs” then “trees” successively, but I choose instead to simply choose “full sun” combined with heights “6-12”, “12-36” and “36-72” feet high. This still left me with 20 candidates for you. The list following are ones I consider some of the better choices, roughly sorted by height. You still need to consider colors and configuration for the best effect.
Rosa palustris (Swamp rose) 6-8 ft.
Amelanchier canadensis (Canadian serviceberry) 6-20 ft.
Asimina triloba (Pawpaw) 10-40 ft.
Prunus virginiana (Chokecherry) 20-30 ft.
Viburnum lentago (Nannyberry) 20-25 ft.
Ilex opaca (American holly) 25-60 ft.
Juniperus virginiana (Eastern red cedar) 30-40 ft.
Acer rubrum (Red maple) 40-60 ft.
As additional information that may help you choose plants to design your plantings, Mr Smarty Plants has had a few questions from your general area that might be useful to consider. This question answer pair considers Trees for privacy, while this one discusses Deer Resistant Species. Finally, for local information it is always a good idea to also consult with the local Extension Office. This link is to the Cornell Cooperative Extension of Putnam County.