We are a team of web designers and developers with 800+ sites for varied business profiles to our credit. Many of them have a custom CMS (in PHP and MySql) integrated with them. Some have Wordpress integrated.
I have read the overview of your requirements and I am confident of delivering well - either in Wordpress or PHP.
I request you to share more detailed specifications - how will friend send an invite? How will a registration be validated that it is through an invite?
I also need to know fields for booking a promo and what happens after booking request is submitted.
I need details about the website design (ref. sites that you like, design preferences, inputs - logo etc.), number of pages (any static pages), any other functionality.
The above details will help me to assess scope of work more precisely and I will revise or confirm my bid accordingly.
I ensure a very thorough job and look forward to hearing from you.