Hi Blankslate. You have what sounds like a wonderful opportunity there
When you say you want to manage the grassland for wildlife, what do you mean? Do you wish to use it as pasture, but with native wildflowers in, or are you thinking along the lines of rewilding, which is a whole different thing? Are there wet areas for a pond or damp meadow? Do you want the grassland management to be tied in with the woodland management? Are there hedgerows around your land or will you need to plant those for nesting birds and insects, and early pollen and later fruit? Do you have cash restrictions on what you can do? Are you hoping for grants or do you have your own funds? Think how much you wish and are able to spend.
You need to think through some of these questions, and many more, before doing something like bringing on animals, whether your own or someone else's.
It would be a sensible idea to have some ideas already in order to make the best use of the Wildlife Trust visit. Make sure their suggestions are tailored to your needs and desires, not just some general, generic wildlifey ideas.
For example, were you to go for a wildflower meadow, there is a huge difference between planting up the whole thing with packets of wildflower seeds which may include flowers and plants which would never normally grow in your area on the one hand, or really learning up about the area, your soil and local climate and encouraging wild plants which are native to your area. The first is relatively simple, but is a bit urban, the second is facilitating the return of your land to its possible 'original' state (in so far as anywhere in Britain can be 'original'!)
Were you to go for wildflowers, then any livestock you graze on the land has to be removed at certain times to allow the grass and flowers to grow and seed, or to be present at other times to graze down the sward. The Wildlife Trust visit could help with this if you know this is the direction you want to go in. It might even govern which breeds of livestock you would be best to keep, some being better at Conservation Grazing than others.
If you are going for wildflowers, or for organic growing, bringing on someone else's stock could be a mistake for two reasons - one in that you would be adding fertility to the grass which encourages the growth of rank grasses and weeds, rather than wildflowers, and secondly, non-organic stock would be spreading chemical residues in their dung, which would set you back in your aim or going organic, and would probably help kill off the earthworm population, which you want to support.
Or your interest might be in providing the right conditions for bees to flourish, either domestic honey bees or wild bee species such as bumble bees and solitary bees, which are endangered. Wild bees in particular much prefer native wild flowers to garden flowers, and also need areas of rough ground for nests.
You might want to encourage wild birds with trees or pasture, or keep wild boar, but whatever it's to be, do your research now and mull over some ideas so you are prepared for your Wildlife Trust visit.