I recommend that you use standard Auras without location. This will mean that you won't need to remake the Auras if you move location.
To put standard Auras into channels, you need to use the "Aurasma Developer Studio". This is a free web app for creating and managing Auras. Please fill out and submit the form on http://www.aurasma.com/partners/advertiser
Regarding how to share the channel - I'd advise making your channel public with a searchable name, but also providing a "subscribe link" on, for instance, a web page.
We can provide a limited number of "Super Auras" that will work on users' devices without them needing to subscribe. Because numbers are limited, we will not currently be able to have an entire exhibition available by default. However, it is plausible to have a "gateway" super Aura, for instance your exhibition flyer, or a particular image near the entrance of your exhibition that the user can tap to subscribe to the rest of your content.
Another option to consider is a "skinned app". This is a version of Aurasma skinned with your own branding, and where you can specify the "Super Auras". This means you can have Auras numbering in the hundreds, and all your users will need to do is download your app - they don't need to manually subscribe. However, with this option, it can take several weeks for Apple to approve your app.
I hope this helps. If you have any questions, please don't hesitate to ask.