Advice in West Devon

[David Dance]

I live in West Devon, just outside Buckland Monachorum, and have a couple of fairly steep fields, full of granite boulders, which have been grazed by sheep, horses and cattle over the years. We are having a ground source heat pump installed, which will require scraping and levelling part of one field, and rather than re-seeding with grass I would like to turn it into a regionally appropriate wildflower meadow. As I have no experience of this sort of thing I would really welcome advice from the group.
The field in question is small (probably only about 2,000 sq. m. in total) and on the side of a hill. The area that will be affected by the current project is even smaller (approx. 450 sq. m.), so I was planning to start with that and extend the area of meadow if successful (we own about 6 acres in total). The farm dates back to the 15th C. but we have only lived here for 27 years so I can't vouch for what happened before that, although the field in question was listed as an orchard in the tithe apportionment of the 1840s. During our tenure it has been intermittently grazed by sheep, but never for long. We get some self-seeded mullein, ox eye daises and foxgloves at the edges, but the majority of the field is scrubby grass with plenty of docks, hogweed and some stinging nettles in places. I have never tested the soil in that field but generally we are fairly acidic round here and things like azaleas and camellias do well. We don't have our own stock, and our local farmer, whose sheep grazed it in the past to keep it down, no longer keeps any sheep, so last year I had to resort to strimming it at the end of the summer.
The work to level the field has already started, so some of the surface soil/grass has already been removed. The work should be finished by the end of April, so ready for seeding then. Any advice on preparation, seed mixes and sources, and maintenance would be very welcome.