Gravity Forms - Post Code Limitation

Hi, I am building a live quote system to allow a customer to come onto my website and get a price estimate for certain products/services. We only work in specific areas so I would like the customer to enter their post code onto the quote form as the first question. I have a spread sheet of the suburbs that we work in, the validation needs to check the post code against the post codes we work in, if we work in their post code then they can move onto the next question. If its outside of our area then the form displays a message that asks them to contact us and tells them they are out of our work area. I am wanting to use gravity forms to do this - you can see my basic set up here - [login to view URL] Just type in post code "3977" to test it. - you will see the suburb dropdown opens up. If the post code is in our work area then the code will go to post code look up table and give the user the option to choose the suburb they live in under that post code and move onto the next step in the form. Now from an admin point of view I would like someone to build this as an installable plugin so I can easily modify the list of post codes and add fields and surburbs via either copy and paste or line by line. I would also like the list to have a tick box that we can tick if we work in that post code area. I would like to have a page in the wordpress dashboard where by I can upload a list of post codes, edit post codes and suburbs and choose if we want to work in that area. These lists could even have their own name so when choosing a list option in Gravity Forms we can select the list. (see jpg file attached - areas we service [login to view URL]) This is the first stage of my quote form, I really need to a plugin so we don't have to modify too much of the gravity form code as gravity forms usually has updates and its better if its a plug in as I will be using this on a few differnt forms. I have also attached a CSV file of all the victorian post codes. I am open to any ideas or your concepts on this project, Basically I just need to have a live online quote system where by I can admister it my self without to much coding or no coding. Happy to get a relationship going with a free lancer to keep adding to it over time.