I would start by planning where you want paths (grass or otherwise) and any interesting viewpoints. Then start to plant the trees as they will take longest to mature. Enrich each planting hole/bed rather than trying to improve the whole plot. Use willow, alder and other species that like damp/boggy soil in the moist areas. As the grass grows, just mow a pathway, not all of it.

You've got a super start with that lovely tree - is it a cherry?
You need to make a sketch map of what you've got and decide what zones you want to have. If you have a lot of trees it will be very shady. It would be best to have a mixture of sunny areas, part shade and shade, so you need to group the trees together and have space in between the groups.

Re soil improvement, I would just improve small areas where you are going to plant, if you're going to plant something fussy. Tree roots go down much further than you could improve anyway, so there's not much point in trying to improve those bits.

As you are going to need lots of trees and bushes I would suggest that you go for bare root plants. The planting season for these is November - March, whenever the soil isn't frozen. As you've missed that window for this year it gives you lots of time to plan what you want to do and get it right. Pot grown plants cost MUCH more than bare rooted ones. Trees that are planted as "whips" get going more quickly than those that are planted as older, larger specimens, so soon catch up and may even pass those that were more mature when planted. And they take less looking after in their first couple of years, when watering properly is important.

As a general rule, native plants are important for wildlife, so you may well want plenty of those.

Take your time and plan what you want to do. It will take several years to get such a large area planted up and as you'd like it, but it's the doing it that's the fun part.

Good luck with a very interesting project.

You have a wonderful 'blank canvas' there, Shads.
Personally, I would just go for localised soil improvement rather than trying to deal with the whole field. If you sread muck over the whole field it will encourage the grass. Put some muck into the planting holes for trees and use some of the same if you are creating any beds. If you are thinking of aconites, wood anemones or similar small woodland plants then I would make scrapes in the grass to sow seed or insert plants. Bulbs can just be planted under the turf.

Well we all agree that you don't need to try to improve the whole field, anyway!! :-)

You also need to check that the land is not viewed as agricultural. If it is you need to get permission for change of use before you start doing anything. Otherwise the planning authorities can make you remove every last tree, shrub, bush, flower and return to the state it was in when you started... Sorry to be a wet blanket!

What a great opportunity Shads - just what I would love - I wish you every success with it.

What a great site for a wild flower meadow - and the area used for that should definitely not be improved. Cornflowers, corn cockle, fritillaries, marsh marigolds, irises...wow you can literally have a "field day"

I have sent you a private message re this question, so as not to bore others.

Many thanks to all who replied and commented. Lots of useful advice, and appologies for delay in getting back to you.

I am actually building a small cottage and this is where I have been for the last couple of weeks. I hope it will be completed and I move at the end of June. At present I am still living in London! Can't wait to move.

Am trying to get as much information as possible, learn as much as possible, find out what sort of equipment would be most useful etc. in advance of moving. Some equipment I can purchase now, and I have time to look for good second hand stuff. I have space to store some things in an exisitng stable block on the property - I will not be keeping horses.

Will post progres reports from time to time.