Hi Swepom, nice to have you join us in the forum.
As Richard said it is nice to have some more EU members, I am in Germany and also roughly 7a climate. I would go ahead and graft the apple rootstocks right away.
I Suggest you try out American persimmons. You can try many but to be safe i would suggest you stick to early ripening varieties like Early Jewel so they ripen fully.
Also it is good to consider putting trees that you would spray for pest or disease in a certain area to avoid overspray issues.
Here is a list of nurseries I have used.