Install vmware ESXi 5.1, have existing ESXi 4.0

I am currently running vmware ESXi 4.1 on a Dell PowerEdge T610.  It is installed on the internal SD card on the server.  There are 2 datastores on the local Hard Drives on the server.  Both contain several VM's.

I want run ESXi 5.1 on this server instead of the current version.  How I want to perform this installation would be to remove the current SD card containinig ESXi 4.0 and put in a new SD card and install ESXi 5.1.  I would rather do a clean install than have to upgade the current version.  

My questions are:

Will the new installation effect any of the exsiting datastores?

Will the datastores containing the VM's still be able to opened and run when the new installaion is installed?

I was told I would need to recreate the networking (virtual switches, ip address for the host) will this create any problems for the current VM's?

Is there anything I can do to make sure the existing datastore are not deleted or altered, so that they won't become unoperational?

If anything goes wrong can I just fall back to the old SD card with the current version of ESXi 4.0 and be right back up and running?

Any help would be appreicated here.  If somebody thinks there is an easier way then please suggest it.  Thanks!