I am interested in at least one, maybe two depending on area coverage.

Looking at this as a retired programmer and experimenter, the amount of meta data could become vary large to support the maximum number of values, while almost all will be unused in a normal setup. A 1MByte SPI flash memory is cheap and easy to add to the gateway and will have storage for all of the needed data. More compact storage (linked list, etc.) become a potential update problem, particularly if several nodes are restarting at the same time (after a power failure), and all sending their presentation information.

I think that the configuration of a node should be in the node firmware, so only one control need to be changed when trying something new or changed. This requires the node to tell the gateway/controller what format and data type is being reported at presentation during node start up, or on request.

Based on these consideration - I suggest that the node description be sent at start up and at a request, and contain the data description and name string. This information is stored in a sparse table (fast Access) in flash memory on the gateway or smart controller. Reserve 3 bits for the action (presentation, set, report, get, system and future use), and 5 bits for the value number - 0 is the node, 1-30 data values, 31 reserved. This would give a total packet of 2 bytes destination - routing, 2 bytes data id, followed by 0-28 bytes of payload.