Logo, I don't understand what you are proposing. I read through what you wrote and, for some reason, I just don't get the picture. Maybe that is why no one else has responded.

if i don't remove the lilac suckers whilst the top of the lilac becomes stunted by the wind above the 4ft wall -then i imagine i will eventually have a very bushy lilac hedge?
or ?

I don't know if you'll have an actual hedge; most lilac suckers come up quite close to the parent. I think that you will have a wider but still short, due to the wind, shrub. Since lilac blooms on last year's wood, if that keeps getting whipped off by the wind over the winter, you may end up with few flowers at all. My gut feeling is that the lilac is not going to thrive there.

thanks your answer is of great help to me
-i had not realized that it would bloom on last year's wood, i will try to find a way to give it enough shelter.