I currently have a MAC Mini, which has 1 Firewire 800 port.  I have a 1TB external hard disk that runs at Firewire 400.  Can I insert another external hard drive that runs at Firewire 800?

Here's the deal.  Currently running SL 10.6.8 on a MAC Mini.  Planning for eventual upgrade to ML.  Have a 1TB external hard drive partitioned into two volumes, one volume for Time Machine and one volume for SL which I periodically update using Superduper.  Thus I always have a point-in-time bootable backup on the external hard drive.
The MAC Mini supports Firewire 800.  However, booting from my current external hard disk is pretty slow, since it only supports Firewire 400.  I am considering buying an Iomega MiniMax which supports Firewire 800.  Then, I would use the MiniMax as my bootable backup volume, and relegate the older hard drive to Time Machine. 
So, question #1 is, can I daisychain the new MiniMax between the MAC Mini and my existing external hard drive?  My expectation is that the new Mini Max would run using Firewire 800 and that the existing hard drive would run at Firewire 400 speed as it does today.  If it doesn't (e.g., daisychaining in the Firewire 400 external disk with the MiniMax Firewire 800 external disk ends up running the whole leg at 400), my resolution will be to run the existing hard disk off an available USB port and have just the MiniMax running at Firewire 800.
Why am I going to all this trouble?  That's question #2.  I don't trust upgrades; they always break something.  When I upgraded from 10.5.x to 10.6.x, the web directories got renamed, and all of my web apps 403'd until I figured out what happened.  Plus, I have accounts for other family members, and in order to ensure their ability to use the computer during my upgrade process, I need to have the ability to fall-back quickly to a known-stable version of OSX.  So what I'm trying to do is insulate myself from problems by partitioning the MiniMax into two volumes, taking a Superduper image of my current installation on the Mac Mini to MiniMax external drive volume 1, then upgrading to ML on the MAC Mini, and take a SuperDuper image of that to MiniMax external drive volume 2.  Then, if the upgrade results in problems I can't resolve immediately, I can simply reimage the MAC Mini from MiniMax volume 1.  BUT ...
... I've read that the ML installation creates a "service and support" partition that is different than the startup disk.  I'm concerned that I won't be able to reimage the hard disk in the MAC Mini once I upgrade it to ML because of the partitioning changes it introduces on the startup disk.  Theoretically, I +should+ be able to use the disk utility on my SL system to repartition the disk in the MAC Mini prior to reimaging it from my backup, but I'm considering the possibility that the new partition may be of a type that the SL disk utility cannot identify, and might therefore be unable to delete or even detect.  So I'm hoping someone else has been down this road and can advise me.  Even at Firewire 800 speeds, booting from an external disk is still going to be slow, so I want to be able to restore my SL image to the MAC Mini hard disk.
A little background on me.  I work for a major disaster recovery provider.  I used to have a Mac PRO G5, which I got used, and the first thing I did with it was install a second hard disk, SuperDupe an image from the first disk to the second, and made sure I could boot from the second.  THEN I started using and customizing the MAC.  I really feel vulnerable with the MAC Mini, since it only has the single internal hard drive - sort of like going out in public dressed only in a long T-shirt.  So my whole thing is, I ABSOLUTELY MUST BE ABLE TO PUT THINGS BACK THE WAY THEY WERE before I do the migration to ML.
Obsessive-cumpulsive?  Yep.  Anal?  You got it.  That's why I'm in the DR business.

You may have overloaded the port, following the instructions below it should reset:
+1. Shut down the computer.+
+2. Disconnect all devices and all other cables, except the keyboard and mouse cable(s).+
+3. Disconnect the computer from the power outlet and wait for 3 to 5 minutes.+
+4. Plug the computer back in and turn it on.+
+5. Reconnect the device(s) (one at a time if there is more than one) and test. Test with each port if you have more than one.+