How to format?

I have a couple of Linux boxes that I would like to regularly backup to a 
5 TB external drive.  It seems like it would be a good idea to format that 
drive with ext4.  Can I just do that with gparted?  The drive comes with 
NTFS format.  Are there any issues I should know about?


Which directories to back up?

What really needs to be backed up?  I guess if the system totally failed 
I'd install Linux (Ubuntu) again.  Of course /home is needed, but 
/usr/local and /opt often have programs I've installed and /etc will have 
a bunch of settings.  I guess /var can have some important stuff.  Are 
crontabs stored in /var?


Which software to use for backup?

I guess I want only to have in backup what is on the originating drive. 
So if I have deleted a file, I want it to be deleted on the backup drive, 
too.  I assume rsync can do this.  Would this be correct?:

rsync -av --update --delete /home /usr/local /etc /var /opt /media/me/back


TIA!

Mike