VPS Backup

I am new to the VPS world. I recently got VPS services from ChicagoVPS, and last week, it was the whole exploit thing which led to several of my sites hosted there being down.

So, I have decided to keep an offsite backup. My question is what is the data which I need to backup inorder to ensure that if I move providers / a fresh vps is provided to me, I can get up and running in least possible time.

1. I am using VirtualMin on CentOS 6. Does a simple inbuilt-backup of Virtualmin suffice? Any other directories which I need to backup?

2. I take a backup of the whole VPS ( tar of / directory), and save it in my offsite server. If I need to move providers or restore to a new VPS, a simple untar of the file will work or it will not?

Any help is appreciated.