I agree with previous answer from jynusJynus. MariaDB is pretty straightforward to install and there are many howtoshow to topics to do inplace replacements of MySQL (worry notYou dont need to worry much, all the utilsutilities and commands you know are the same), for For example, from MariaDB site itself MariaDB Upgrade. You can also simulate a MariaDB/Percona/MySQL configuration with your hardware settings from Several Nines site (search for the configurator)
I advise you to do a prior reading in Galeracluster's own site forso that you tocan evaluate if those features presented are really what are you looking for. Personally I think Galera as a great "enabler" for HA on MySQL (and "derivatives") without changing significantly the way you deal with databases.
side notePlease Note:If If your going with Galera (and not NDB type cluster) consider using Percona XtraBackup instead of the proposed rsync or mysqldump for SST (state snapshot transfer)