I would avoid cattle initially until you're sure you want them on there, if it's a wet winter they could trash the new grass. Ideally if there's enough grass to warrant it being newly sown, I would see if anyone wants to winter graze sheep on it. If the fencing is just wire they can bring their own electric reel fencing. It's not a big money spinner but it will do the land good fertilising the grass gently, and ready sprinkled!
We were paid 35p per head per week last winter for rough old fields. That was them doing all the work, water, looking over the sheep, moving fences to the next field etc.
This summer those fields had a lot less ragwort to pull, and the hay yield was better.
NB the first year after seeding it MIGHT be better simply to wait until summer and get someone to come and take a hay or silage crop from it, and pay you for that, giving the new grass more time to establish.
I can't comment on the business/legals stuff, the local solicitors all have agric departments or the accountants, might be worth a half hour chat given the implications of getting it right/wrong.