If you need more a bigger 19 gallon will drop right in and you can pick them up at any Napa auto parts.
No, and in fact you could argue that a 19 gallon tank only provides a marginal extension of driving distance over a 16 gallon due to weight gain from the tank when it's full of gas.
16, if it's still the factory tank. The new tanks, are not as good as the original tanks, I bought a car that had a replacement, it was 6 years old and full of holes. You need to seal these newer tanks.
I would restore an early tank if I were to do it again, only for the added space to run duals... You can still run duals with the bigger tank but not as nicely.