Q: Wireless Setup - Need Guidance

I'm hoping you can help me out with something...

Downstairs with the modem I have an Airport Extreme. 

In one room upstairs I have an Airport Express that I'd like to connect wirelessly to the Extreme, and re-broadcast the signal.  I'd like the enternet port to also be available to plug devices into and attach onto that network.

I have another Airport Express that i'd like to hook up for the other half of the house.  This has the capability to be hooked up with an Ethernet over the Powerline adapter - so if I could plug a network cable into the ethernet port and broadcast this wirelessly, that's the ultimate goal.

What settings should I set on each device?  Someone had mentioned WDS but I am unsure of this setup, and would like to know the best way to do it with minimal impact on the network performance and throughput.

Thanks!