Sorry, I thought I did (maybe between the lines) 
- Yes. However, it's recommended to have different versions only for short time (e.g. updates)
- Yes.
- You can apply the latest patch without applying anything in between.
- Let Update Manger do its job.
- No need to upgrade vCenter in this case (see Interoperability Matrix). However if you want, you can upgrade vCenter Server before or after patching the hosts.
André