capbat
This is just a general thought ; the idea being «Now that you're using a release candidate, there is no point in staying with the first try. RC3 is "better", ie has fewer problems, than RC1.»
As the upgrade procedure does not run any upgrade script of any kind, you should go directly to RC3. the upgrade plugin will install RC3 ; no choice.
this however won't help you with the smallcaps issue. I understand your hesitation. Maybe you're right and it is better to wait for the final release....
The backup plugin only backs up your, config, template... You need a full backup to rollback a failed upgrade. The easiest way is just to backup your whole DokuWiki directory.