I am trying to hide certain tabs such as Storage when requesting a new VM
This is very similar to another forum post (https://communities.vmware.com/message/2724573#2724573)
So far as I know the only option is to use a XAAS blueprint to sit in front of the composite blueprint and launch the deployment via another workflow.
In current versions, that is correct - XaaS used to "wrap" the catalog request. There are plans in next release to make this easier.