Posted: 10/08/2015 at 16:00
Not a good idea to bury the tree's roots under extra layers of soil either.
If the garden is that big, you can surely find space for veggie beds in full sun which is what most need - except salad leaves, chervil, parsley. Rhubarb can cope with a bit of shade but needs deep, rich, moisture retentive soil to do well.
I suggest you spend the first year in your garden noting what is where, what you like; what you don't like, when they appear and disappear; when the sun gets to each bit at different times of year; what needs to be lifted/divided/moved/swapped with mates or binned and so on.
Then you can make a sensible plan of what and where to grow and what you need to do or buy or sow to achieve it. In the mean time, weed and feed and mow and prune to keep it looking as good as can be while you get to know it.