Hi -- I know some of the answers to your questions. American plum self-fertile -- seems to be. I had 2 and then cut down one after it got old and started to go - the other still seems to bear well. There are other plums around the yard, plus various wild Prunus species in the neighborhood, plus various oranmental plum and sandcherries in the neighborhood as well. 2) 5 x 5 foot size. Yeah, I don't see a real problem with it. My 2 American plum seedlings grew naturally to about 7 to 8 feet max, with probably a 6 to 8 foot spread. So, with a little pruning, probably not too much of a problem. 3) Partial shade -- definitely. My surviving one is in about 2/3rds shade now, as the trees around it have gotten larger, and it seems perfectly happy as an understory type tree. It still gets pretty good light because the two trees near it are a Kentucky Coffe and a Sycamore, and both don't start to branch until very high off the ground. 4) Taste -- Well, the fruits of my plum are quite tasty when fully ripe and slightly soft. They have a bit of astringency when not fully ripe. They make wonderful plum sauce, jelly, baked tarts, etc. I've never had the Chickasaw plum, so can't comment. I did plant a beach plum last year, but it's still only a foot tall.

I do not recommend it. You may get a delayed incompatability. About the time you get a good fruit set, if at all, the branch will break off. Better to graft Europeans on to Europeans. Even if it did work, the vigor is not the same. I lost two Puget Gold Apricots from Graft Incompatability. The Nursery used some prunus root that worked 'for a while'. Here is a link that might be useful: Home Orchard Society

I grew them here in Arizona. Low chill, early bloom. For the first few years, I had two plums on a huge tree grafted on Mariana -- so it needs a pollenizer if you want more than a few plums. It definitely has an acidic/tart aftertaste that I didn't care for, which is probably why it was never a commercial success.

had to google caliper lol I'm pretty sure you mean Prunus angustifolia because that's the only one I see get called Chickasaw plum but there's also Flatwoods/Hog plum, Prunus umbellata. I have P. umbellata and it was over 5' 6" feet when i bought it (this is a species that can be sour tho) from this place in Jax http://nativeanduncommonplants.com/ I fertilized it in mid to late summer again with citrus fertilizer and it responded with a second burst of growth about equal to initial spring one so you might be able to experiment with that to get it to grow faster. Not sure what its diameter size is, sorry. It's certainly thicker than my thumb, though. Edit: I've never ordered from these people but i have considered it. https://www.wilcoxnursery.com/plants-and-supplies/trees/chickasaw-plum-15-gallon/