The offer is to invest 2.5M in exchange for 10% of the company. There is no offer to buy all your shares for 25M.

It's absolutely abstract! Who is this buyer, does he really have the money, is he going to follow through, is this legal?

In principle, these models can be run a la 'ab initio' (from first principles) so no fitting is required. Of course, there are subtleties and unknowns, so some fitting is needed, but overfitting can be checked in the usual ways.