The wall doesn't look solid enough to me to retain a bed for either a tree or shrub. Also the soil is mounded up in away that is likely to wash out in future. Are you intending to improve the structure before planting? If not I think you'll be fighting a collapsing bed in due course. .

The top picture is too blurry to get a good view. If each of the leaves divide into three leaflets, then what you have is Poncirus trifoliata or trifoliate hybrid that may have been used as the rootstock for some other citrus variety that later died. If this is the case, the fruits are probably going to have a very bad flavor, and would be what some might consider an "ornamental", since it won't be good for eating.

I grew up in Bucks County and had pawpaws there in my parent's yard. I now live slightly north in New Jersey and have had pawpaws growing here for quite some time. They grow easily. Start with potted plants (not bareroot).....they have roots with little root hairs and it is hard for bare roots to survive. They start out slow the first year or three and then take off. Plus is the large tropical looking leaves. The bark is smooth and attractive. Of course the fruit is a plus too.....it is very good (well most people love it, a few will hate it). My yard is small so I originally planted two trees close together. Negatives, which were mentioned, they do get root sprouts as they get older..........and between that and seedlings (from fallen fruit) you end up later with pawpaw sprouts everywhere at least close to the parent trees. I like them though!!

Snowflake Tree is now Heart Tree. I was sad taking my snowflakes down, so decided to replace with beaded hearts. My dad has been recuperating at our house the past few days (on our sofa, which faces the display) and he said it made him smile every day. :) After Valentine’s, no more tree until next Christmas. I’ll miss it! This one inspired by a dear friend who loves southwestern decor: This one inspired by another dear friend who loves anything coastal: I made my dad this one for his house: And this one for my sweet sis-in-law (the lightest beads are a pretty shade of pink, but look washed out here):