Is this as easy to do as it seems, or are there any issues I need to pay attention to?
We should also mention changes in administrative procedures and scripts that are external to Splunk, but control Splunk, e.g., start and stop scripts, backups, archiving scripts, etc. for example, you should generally make sure to offline indexers rather than force stop during maintenance.
You absolutely can migrate your indexers to a cluster. You'll want to enable them as cluster peers. But first read this topic for a few issues that you should take into account when you do so: