Cost per flying hour would be a bit of an issue for Typhoon, sadly.
Typhoon - £70-90k/hour a few years back.
Hawk T1 (Red Arrows) - £6k/hour
Hard to see how the answer shouldn't be a Hawk T2. Being UK built is part of the overall media/
PR package.
I don't think many in the public really care about the marginal cost of running the RAFAT.
And as for numbers - it has to be nine if for no other reason that the Patrouille de France have eight aircraft