Modification to HBook System (Wordpress) - Payments and Reminder Features

Purpose: we are a short and medium stay accommodation provider renting out properties to travellers around the world. The stays length ranges between 1 month and 24 months. We are using HBook – a WordPress plugin booking system as the basis of our booking system. The purpose of this project is to add additional features to that software. The software is primarily used through the back-end and reservations are added manually by our team and not through the front-end by the guest. Summary of features: 1. Allow the selection of a calculated security deposit of 2-weeks rent instead of fixed value or a percentage. 2. Create a payment schedule (plan) for every booking and send it to the customer when we create the reservation. 3. Create payment reminders to the guest and to us based on the payment schedule 4. Visually display the payment schedule on the reservations grid adjacent to the reservations. Please see attachment for full information. You must include answers to these questions in your bid to be considered for this project: 1. Have you done any development work on HBook or modifying Wordpress plugins before? 2. Have you done any development work on hotel booking systems or real estate rental systems before? 3. Do you prefer to submit large diffs or small diffs and why? 4. Have you created design docs (what you're going to build, what the feature requirements are, how you're going to set things up, which functions you're going to need, data structures) for your projects?