Im using a melee monk. + Str Charm. I put 120 in dex and the rest in str. Is this correct? I use Staff and robe armor with 100+ ee on both.

I would say to be most effective you should stat all Dex, and replace your strength charm with a Dex charm.

You can stick with the EE robe if that is what you prefer, but if you tend to usually be at the back, I would say also replace these robes with Dex robes.

I thought 120 dex was max for best dex bonus?

Nah, prior to the most recent update some people would recommend that you get 120 Dex.

Now however there are ratio's on Weapons. And on a Staff the ratio is 25 Str/75 Dex, so for your monk it will benefit you most to go all dex