Crazy CRAZY plan Brogins, you're going to be knackered!
But go for it!
Donny to Cadwell should be less than 2 hours, and I would recommend the same place to sleep as redruth is talking of. It's safe for the bikes and you get a great breakfast before you leave.
Tyres - I managed 4 track days last year, plus a bit of road riding, on the same set of tyres. They were getting a bit tired at the last one and probably should have been replaced. So like JPM says, be ready to replace the rear.
Have fun!
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