I got lucky and happened upon some jamun fruit at temple. I'm certain they weren't imported because this type of plum isn't sold nearby. I've actually never seen it in CA. I cleaned and dried the seeds and they're ready for propagation.

Does anyone know what size pot I need? I have the soil mix already -- it's so similar to cactus soil I'm just using my dragonfruit mix. Thing is I don't want to have to transplant this one. It's a tree, so I want it in a suitable pot from the start. I'm thinking one between 4 - 6 inches wide would work, but I really don't know for sure. I have a few lagers pots but I don't want to use them if they aren't appropraite. We all know the issues there.

Thanks for the help.

I suggest you start them out in containers such as these: https://www.ebay.com/itm/2-NEW...

These are containers I use to start trees and bushes from seed: no point planting them in anything larger because nobody can say how many of those seed are truly viable and how many seedlings will develop properly.
Once you have healthy, well developed little trees you can move the best-looking into nursery containers such as these: https://www.ebay.com/itm/Premi...
I only use 10-15 gallon sizes, but if you plan to quickly move your Malabar plum to a better looking container you can go for 5-7 gallon sizes. Know however if the tree is growing properly the rootball will soon fill the whole thing.

Now for the bad news: Malabar plum trees grow large, like in really large. Once you have your nice looking little tree in a 10-15 gallon container you should transplant it in the largest container you can find. I have a 60 gallon nursery container which I think would be the minimum size for such large trees and, believe me, it's not easy to move it when it's filled with moist soil unless you work with at least another person and both of you are pretty strong, so put it in a palce where it will stay for a long time.

I ended up using small seed starting pots. The ones on top are all dragonfruits, and thebsame pots I used for the jamun seeds. Similar, but not identical. I have them inside out of the sun for now. When they breach the surface of the soil I'll put them outside. They were 100 for around $12 on Amazon.

Anyway, Inagree and I appreciate the feedback. I'm still pretty new to raising potted plants, edible plants in particular. I'm glad to know I'm doing things right :)