I'm planning a c 36ft pleached hornbeam hedge to bisect a kitchen garden which is part walled, part yew hedged around.

What distance apart does anyone recommend the hornbeams to be planted? I was going to go for 8 trees just under 5ft apart (ie with 34 ft between the first and the last), and the first and last about a ft away from the yew boundary. Is this too far apart? Would 10 trees just under 4 ft apart be better? I'd prefer to have an even number to maintain the vista along the central path through the hedge.

Also what height of tree does anyone think is optimal, balancing good initial height with trainability and ease of establishment of the trees?

Many thanks