Scots Pines can do remarkably well in small pots as the attachment below of a Scots I am working on shows. Excuse the old picture taken after the second styling, I really need to take some new ones. Anyhow, if the roots are good, they don't seem to mind at all, the Scots shown has been in the Horst pot for over two years now.
I think if it were me, I'd have it in nearly pure pumice growing in a colander some such. It's going to need some serious root development and it's not going to get it in a bonsai pot. Just my two cents worth. good find.