Before you can begin trying to implement DataAssist for the inserts and updates you will need to have your db structure defined.
Based on what you have posted I think you will need to have a userID column in the following tables:
6. Corporate Days
7. Inspirational Locations
8. Special Offers
9. Eating Places
10. Spa and Leisure
The following tables will need to have a column to hold the listing id:
4. Meeting Rooms
Once you have these tables properly crafted you will use DataAssist to generate a set of pages to manipulate the data in these tables. DataAssist does not incorporate your requirements for data integrity, this is something you will need to take care of in the design of your pages. For example since you would like to have only one listing per user you should do a check of the listing table for the current user to ensure that a record for that user does not already exist.
From the perspective of the user rite now it would go like this:
A new user registers
Once logged in the user can add a listing
On the insert page for the listing you will bind the id for the currently logged in user with the userID column you have in this table. This is the same for the other tables that have the userID column, it will be bound to the id for the currently logged in user.
After the listing has been inserted you will have the id for that listing record available from the session, you then make sure to reference this session variable for the listing id when inserting into tables 4 and 5.
Please post back with any questions that you have about creating the pages or using DataAssist to edit the insert and update statements. When you reply make sure to post questions about the functionality from the perspective of the end user that will be interacting with the pages, I find it much easier to address situations when questions are posed in this way.
As far as obtaining your files to evaluate and offer guidance that really goes beyond the scope of the support that can be offered. I can address specific questions about use and functionality of the tools, or how to implement certain features in the context of our tools but tutoring or guiding is not something that I can provide.