ESXi 5.1 has raised the limit on datastores to 64 TB.
The VSA has a limit of 24 TB total for all datastores. The release notes have the maximums. VMware vSphere Storage Appliance 5.1.3 Release Notes
The need for 10Gb would depend on your requirements and expected workload. I would deploy storage with at least one redundant link, 10Gb or 1Gb.
Here is a quote from the VSA admin guide "All hosts in the VSA cluster must have two dual-port or four single-port network interface cards".