We have a yacht brokerage website and I currently use the tab widget to create a holder for each boat for sale and I load it up myself.
I would like to automate this process and have a brokerage page were a client can register with us, fill out an online form/template and add photos and videos and publish it to our website automatically. Is there a widget, template or online service that can help me achive this?
You will not be able to achieve this with Muse.
That will require a significant amount of server side coding such as PHP and MySQL. This is beyond the scope of Muse and not supported.
That's what dynamic systems like Wordpress, Joomla, Typo 3 etc. or web commerce systems/ online shops do. Simply sign up and pay for a pre-configured hosted installation of such a system, pick a nice them and manage your content and users. Of course you can use all sorts of third-party widgets or sign up for a Business Catalyst paid plan, but in the end the effort to hack everything together and maintain a site that still might not give you al lthe features as you want them will be more frustrating then perhaps compromising on styling options of pre-existing skins/ themes on other systems, but with much more power under the hood, namely easy management of a client/ user database.