A minimum of a 3 Node Galera Cluster is Recommended, but is it better to have 5 nodes?
If the criteria for "safe" is "no single point of failure", then 3 suffices.

If "safe" means surviving "any two points of failure", then there is no solution.  5 only handles the case where two servers go down, not arbitrary combinations of things.

RAID 10 (or 5, but not 1 or 0) provides recovery from a single disk failure on a single machine.  Since a 3+ node cluster can survive the failure of one entire disk subsystem, RAID is not required; it just gives you an extra level of comfort.

I do like RAID 10 with Battery Backed Write Cache -- this has the bonus of making writes virtually instantaneous.

Here is a situation that can happen with a 3-node cluster (N1, N2, N3).  Let's say N1 dies.  After putting a new (or repaired) N1 into the cluster, it will rebuild the data.  This uses N2 to as the 'donor' to rebuild N1.  That leaves only N3 at full functionality.  (N2 will be somewhat busy sending data to N1.)  The Cluster is still alive, though "slowed".