Setting up new network _ ethernet and wireless

Hi All,

For a while i have been running 1xAEBS and 3x Airport Express. They are set up like this:

My cable modem conects to the AEBS and the 3 express's and set up via WDS to extend range and provide ethernet access for a Playstation, an older imac and run a printer wirelessly.

Now my problem is that and the far end of my network (the imac) i am only getting 10% of my 10mb internet speed which annoys me. Obviously this is as the signal is be relayed via another airport express and all the thick walls and such.
so i am going wire up the house with cat5 and a switch and put ethernet sockets in each of the rooms where the is currently an Airport express.
If i were to do this and connect an ethernet cable from my new sockets to the airport express am i right in saying tha these would the act as access points for me to wireless connect at full speed?

If so could you give me any advice on how to configure the expresses How can i be sure it is connecting to the AEBS via ethernet and not wifi?

thanks

Jon