Clemburt
I assume you use the BT HH as effectively a modem and the AEBS as your router?
To connect a switch to an Airport Extreme you just connect your LAN cable to one of the 3 ports on the back and then connect the other end to your switch, there is nothing complicated about it, no configuration required.
Then connect all your Sooloos components to the remaining ports on the switch, as for choice of switch there are so many I can not advise you on what to select, personally I have an 8 port Cisco unmanaged switch that cost around �30.00 and has given me no problems.
Cheers
Russ