Welcome to the Commuity,
some thoughts about the steps you mentioned.
0.1) check the VMware Compatibility Guide to see whether the old hosts are supported
0.2) review the VMware Product Interoperability Matrix to see which host versions are supported by which vCenter Server version
--> 1.) Update Manager is included on the vCenter Server installation iso/zip file. You need to use the version which comes with the vCenter Server version you have installed.
--> 2 and 3) See VMware Product Interoperability Matrix
--> 7) Why only one beer?
André