Primitive sheep will have the time of their lives - they thrive on rougher grazing and love to browse. Cow parsley is great for all sheep, at least when it's short, and it's SO beautiful when it flowers. Rosebay willow herb is a plant of bare places, so tends to take over when previously cultivated ground is left to go wild.
I would advise that you take a year to see just exactly what you have on your land, plant and flower wise, and what the grass is like throughout the seasons, including which grass species you have. Looking at it now will give a different picture to what it's like in, for example, springtime. Maybe confine your animals to only part of the land for that first year.
Pigs - piggy people will come to answer that question more fully. We kept Tamworths for a while and they are certainly good ploughs, but I don't think all pigs are. Anyway, Tammies are more beautiful that any other pig breed, in my eyes anyway

Can it work? - absolutely

In addition to your new smallholding you will have a wonderful wildlife haven, which will give you endless pleasure. It sounds lovely.