Customize existing Wordpress directory plugin

We have implemented a directory plugin for our website that is written by a third-party developer who's not available to implement customizations to it that we need. The successful developer for this project will: 1. Become familiarized with the codebase of the plugin in order to make updates and changes to it. The plugin supports use of customized templates in our own theme. Ideally, all of your edits and customizations will occur ONLY in our customized templates, and not to the core plugin. This is a MUST as we need to keep the plugin updated over time. 2. You will work to implement the customizations in a way that is unlikely to break in future versions of the plugin. While I understand you cannot guarantee this, you must be familiar with best practices in design and implementation of extensible plugin changes. 3. One customization will be to implement the loading of external PHP scripts when a new search is performed by the directory search box. Currently this search is fired off in javascript and via AJAX, updates just the directory listing. I need the search to also make a call to 2 different additional PHP scripts and load them according to the variables changed in the search box, all on the same page. These scripts are currently called by the third-party, unrelated Ad Inserter plugin, but you're welcomed to call them differently if it makes more sense. 4. A second customization will by breaking the "Add a new listing" form into 5 separate pages (it's currently all on one page), with a progress bar on top showing the person's progress through the form. You MUST complete the work within the timeline specified. If you say you'll complete the work in 1 or 2 days, that's completely unrealistic for the scope of this project and I won't even look at your offer. This will take some time to familiarize yourself with the plugin and code, and figure out where to make the changes needed that will be the least likely to break the plugin in the future. You MUST agree to provide at least 6 months of support for your work, in case a future updates breaks your changes. Please ensure you bid knowing and agreeing to this provision. You MUST be completely familiar with Wordpress plugin architecture and agree NOT to rewrite the entire plugin that I need these customizations for. If you have not read the project description to the end, I will not accept you for the project's bid. You can signify that you've read the project description thoroughly and understand what is being asked of you by putting this phrase in your reply to the project bid: "I am grateful for sunshine." (I do this because I do not like automated bots that reply to all new projects with a bid without ever having read the description.)