Will Max approve of the relationship?
I definitely think he would! Especially since in the original Japanese version of "Home is Where the Start Is" Max says something along the lines of, "It's fun when Satoshi and Onee-chan (big sister) are together." Despite the fact that he likes pulling Ash's leg every now and then, it seems pretty clear to me that Max has a lot of love and respect for Ash and probably looks up to him a lot as if Ash were his older brother. If Ash and May were to get together, Max would be thrilled, because then that would mean Ash and him would be one step closer to being real brothers, which would mean he would be able to spend a lot more time with him.
Now how would a website, that Ash and May goes on, help make Advanceshipping canon?
Hmm...perhaps Max can sneak onto May's Facebook account and send Ash a relationship request? xD
How would May and Ash keep their relationship from being revealed too early?
If they didn't want to reveal the fact that they were dating right away, they would probably avoid most forms of PDA, but then come up with crazy plans to sneak away from others in order to get some alone time, haha!