The only pokemon I played was the original, with 151 monsters. I can proudly say I caught them all. 450....eh...I'm not sure I'd catch them all.
It seems you will probably be spending some time hunting down, raising, and breeding monsters, though to get this 100%.
You can find me on facebook as Markus Van Rijn, if you friend me just mention you're from VGchartz and who you are here.