Starting updating hosts

I apologize for the very basic questions.

I need to start updating ESXi 5.x hosts in a vSphere 5.x environment.

Update manager was installed when the infrastructure was mplemented but up to now it was used only to download patches, not to apply them.

• I plan to start applying patches to hosts, but I need to protect each host as they are used in production.
  
  • How can I protect each host from possible problems (i.e. a patch causes an unexpected problem and the host does not restart?)
    
  • Can I backup the host or at least save the host configuration in order to restore it in a very short time if anything goes wrong during update?
    
• Given my hosts are all 5.x, how can I avoid downloading patches related to ESX or ESXi 4.x?
  
• At the moment I need to apply urgently only a limited number of patches: how can I check if they depend on other patches or can be simply installed?
  

Regards

marius