Suggestions:

minimum required for inventory use case
list-gateways
list-tags-for-resource

likely useful to fully understand the resources a gateway "owns"
list-local-disks

for s3 gateways (required for my current investigation)
list-file-shares

for fsx gateways (not currently required)
list-file-system-associations

for tape gateways (not currently required)
list-automatic-tape-creation-policies
list-tape-pools
list-tapes

for iscsi/volume gateways (not currently required)
list-volume-initiators
list-volume-recovery-points
list-volumes