Can I daisy chain Thunderbolt to FireWire 800 to FireWire 400 If I had a FireWire 400 DVD drive connected (via a FireWire 400-800 cable) to a FireWire 800 hard drive that was then connected via a Thunderbolt to FireWire 800 adapter to a Thunderbolt hard drive, that was then connected to a Mac, would I be able to use all the drives?
And would I get Thunderbolt speeds on the Thunderbolt drive and FireWire 800 speeds on the FireWire drive? 
Also all the drives are powered externally.
Your setup will not work. You must have separate FireWire and Thunderbolt chains, and not connect devices to both interfaces simultaneously.