Can you start doing that then? Do as many as you want. There are some exceptions, however. These you don't have to worry about:
Onix/Steelix
Magikarp/Gyarados
Cubone/Marowak
Those are all the ones I can think of for now. Don't worry about doing them.
If you use D/P sprites, resize them to 80/80 using nearest neighbor.