The recordings are something like 60-100mbps bitrate, XAVC-S or whatever, so 1 gbps network speed is perfectly fine. The latency will suck though, i mean each time data is requested it's gonna be some time until it's read by the nas and the first bytes come... unless the nas storage is SSDs.
It sucks that DDR4 memory is expensive. If it were cheaper, a solution would be to buy a few 8 or 16 GB memory sticks and fill that board with memory. then use ImDisk Virtual Disk driver (this one I use because it's open source) or some other software to create a RAM disk and load all the footage into the ram disk when you start editing on a project. Then you won't care if you use SSDs or regular mechanical drives, everything's in RAM.
For example, a 8 GB stick is 75$ and 16 GB sticks are 150$.
Dave, you have that dual xeon machine, which should have plenty of memory slots. If it accepts unregistered DDR3, you could just fill those slots with memory and set up FreeNAS with a ton of RAM caching, so once Vegas starts requesting data from a file, Freenas would cache the file to RAM and then you'd have very snappy timeline, faster rendering etc.
8 GB memory sticks are cheaper as well, something like 50$ each. And registered ecc ddr3 is cheaper on ebay, i see for example 16 GB (2x8) for 92 australian dollars on ebay , here's
an example or
this one for 63$ for 2 x 8 GB DDR3 1333 mhz registered ecc
If anyone cares, here's the overkill solution LinusTechTips has ... though they record their Youtube videos and other projects for various clients in 8K 60fps with RED cameras: