Wherever you go in the uk it seems to grow, it self seeds freely. It is brilliant for habitat for certain things. E.G greenfly, aphids-ladybirds and birds. Yes boring when there is too much of it. However I don't buy the whole native idea. We have excellent non natives such as the redwoods, monkey puzzle etc, If these species get wiped out in their native habitats, they could be restored by uk seed.
I have thought for a while now the need is to plant trees as a whole, we are more desperately in need of trees for many reasons, flooding, soil erosion, habitat, timber supplies, air quality and so on.
If we all stuck to the prevalent attitude of native we must, native its not diversity as a whole.
Sycamore is not a problem tree like willow for example in New Zealand this was introduced and is a weed everywhere along with gorse and troublesome.
If someone had planted Elm in the uk in the pre 70s what would they have now. Conker is going the same way it seems.
I suggest plant up to 80% sycamore if you want for coppice and can get transplants cheap enough and eventually to grub out. Space the other 20% with native to leave a nice mixed woodland for future generations. Maybe the odd specimen of foreigners as well.
I personally dont subscribe to all this idealism conforming pressure, think outside the box. Its like when the hedges where removed to make fields bigger, now they are replacing them. and a real bugbear is why do we have to waste resources at hedge planting at a nearly impossible in many situations at 6 per metre? Stock proof? What in the middle of arable country or roadside? How often are they laid to restockproof? I would go up to a metre apart for hedging Thats probably the survival rate at maturity.
My point, Your land you can do good in many non conforming ways. I wish I had the assets to plant my own woodland my way.
I wish you well have a good think get a few ideas. If winds of thought change cheap trees can be stripped out and a lucrative set up could be done later. We need timber we need trees.