I have specified form configurations for my custom aspects in my amp's share-config-custom.xml file.
We are planning to use standalone UI not share interface, and I'd like to access the field-visibility & appearance information I setup for my aspects.
Since the xml file is in a share amp I'm looking for some kind of Share API to allow me to query for it.
Go read about the form service. Then look at the Share tier and repo tier web scripts that are leveraged as part of that. Your custom front-end can probably reuse those.