Airport Express to replace BT HH3??

So I'm currently on BT Infinity. My current setup has me connecting my open reach modem to the BT Home Hub 3 (which is a piece of crap)..

I connect to my router via Wifi only and do not use any of the Ethernet/USB ports hence why I'm considering the Express over the Extreme.

So my question is can I plug the Express to my Open Reach modem getting rid of my homehub altogether? and also will I get better internet speeds over wifi if I opt to get an Extreme or will it be the same as the Express? Please keep in mind I only need the wifi capabilities.