OK for now I have finished and these are the results: it works great. the problems of leaking fuel and the loud popping sound have been solved with new gaskets. The problem with WOT was indeed due to restricted airflow. I replaced the sponge with a paper air filter, which is what these new photos are of. So now the bike runs great, quiet, powerful as it's ever been, and I'm happy with it. The whole air intake silencer as it is right now is a first try, so it was built with function in mind before looks. But now that I have good function, next step is to make it look good. I saw some high-airflow filters that looked like KNN filters, which are what I will probably move up to, just for the good looks. Also, the grey box has gotta go, since it no longer serves the function of housing a sponge.
I would however, still like to make the chain noise quieter, although I don't know if that's possible. Maybe a little grease, but the sound has always been there even when it was brand new. So if anyone has any input on that, that would be great. I'll also search the forums for more info on chain noise.
Thanks to everyone for all your input and help!! I love the new sound of my bike!!