Sharing cluster switches is not supported or supportable, sorry.
I would suggest to setup as a 2 node switchless cluster, then expand to 4 nodes when you get the additional switches
In 9.3 we remove the ability to specify the name of the cluster you wish to join, so you'd have to monkey around with manual vlan configuration etc (and ideally a second set of links between switches). Not the way I'd want to run my enterprise storage system..