Any really as most bare root tress will be grafted standards.

Perhaps ones trained as espaliers?

Make sure you look up what pollinates what before you buy your apple trees. I have a row of ten fruit trees on dwarfing rootstock and they vary so much in habit and fruiting. Growing them cordon fashion, at an angle, on wire supports, is another way of forming a barrier. They are said to fruit better, and easier to prune, as not so tall. Mix up early fruiters with late fruiting trees, cooking and dessert etc.....but make sure they can all be easily pollinated.

Yes, espalier or a row of cordons would make a splendid barrier. Make sure you have strong, possibly rot proof stakes (metal?) as they are difficult to replace in 5 years time when the trees are established. Try to visit a nearby fruit garden (National Trust etc?) to see how they are grown. And study the pruning methods. What a great project!

Thanks, food for thought, greatly appreciated