Using MPIO with multiple 1GB is a good way to go.
The 10GBe connection for replication will also be advised.
In the future when adding more ESX, you can easily add another 10GBe and use that instead of MPIO connections.
No limit to NIC configuration from our side, its more hardware limited than anything.
Ping nodes should be equipment with 100% uptimes, and can be reached from each DSS V6: http://blog.open-e.com/ping-node-explained/