Fencing trees

I’m planting some fruit trees as well as oak, tulip poplar, hazelnut, coral berry, and one or two more. This is my first “improvement” on my father in laws property that I’m due to inherit at some point.

The 4 fruit trees are about 4ft tall, but all the others are 12-18” seedlings (even 12” may be a stretch for a few!” All bare root.

I put 4ft tall x 5+ft diameter circles around the fruit trees. Metal wire fence was on the property.

How big should I go with the other 20 trees? I need to buy new fence and posts and want to keep the costs in check.

Is 3ft fence tall enough? 3ft diameter circles?

The property has heavy deer traffic.