You can easily get 99 FM with that. All you need is like 4-5 mill. If you are members, just buy 4-5mill worth of maples and then use a bot or do it legit and you got a 99 right there...
Not sure. To be safe and for myself to not be wrong, the price is around 4-6mill... Not that much for a 99. But for the Firemaking, IT IS NOT WORTH IT FOR THE DOUBLE EXP BECAUSE THE LOGS ARE GOING TO BE MORE THAN WHAT THEY USUALLY ARE!
Then you also have cooking, not sure how much that would cost but I know it isn't goign to be cheap because of the double exp.
I would prefer FM but your choice, if you want to spend the extra money that the econ has added to the logs then fine. You have more than enough money for Firemaking.
Not sure about Cooking though.