NUMA config - sp_blitz output
You have two physical NUMA nodes (Memory Nodes), with Automatic Soft-Numa dividing each one into two NUMA nodes in SQL Server.

I'd like to understand the meaning/importance of VAS Reserved

Virtual Address Space (VAS) is reserved as a first step to allocating memory, see: Reserving and Committing Memory.  For 64bit processes the VAS is immense, and so it's common practice to reserve a huge block of it for later use.  This doesn't allocate any physical memory, it just reserves a contiguous range of VAS.  Later the application will &quot;Commit&quot; chunks of this address space to map the VAS to either physical RAM or the page file.
And in a NUMA system the memory allocation happens on the same node that the code is running on.  So that query just shows that a large VAS range was reserved on Node 0, probably at startup.
But SQL Server also supports a secondary method of memory allocation using the Address Windowing Extensions APIs originally added to Windows to allow 32bit applications to address more than 4GB of ram.  AWE allocations have the benefit of being exempt from the Virtual Memory Manager paging.  SQL Server calls memory allocated this way Locked Pages, and will use them if it has the Lock Pages In Memory permission.  AWE allocations won't show up under Reserved or Committed VAS, and are tracked separately in SQL Server's DMVs.
To to see the total amount of memory in use by a node you need to add virtual_address_space_committed_kb and locked_page_allocations_kb
sys.dm_os_memory_nodes
And, no I have no idea why sp_Blitz reports on VAS reservations instead of real memory allocations.