The Hortonworks Sandbox is a great way to get introduced to Hadoop and to "get up and running in 15 minutes", but at some point in your platform architect role (see disruptive possibilities (the rise of platform architecture) for more details) you will want to built out your first multi-node cluster. Using Ambari will be a great "wade in" approach to this next level of Hadoop administrative activities.
Check out Build a Virtualized 5-Node Hadoop 2.0 Cluster for some help if you're ready to take this next step.