Development of a new website

Hi there,hope your well!

I'm looking to have a website developed. It would feature member registration for user and also business.
Business users would be advertising events and services to registered members. Such as restaurants.
Users would be able to search and buy from the registered business, invite there friends into the site to make them part of the purchased event. The users would need to transact through the site seamlessly through a chosen payment gateway with the use of an API.

I have a full specification for the site but above is the basic concept.

Thanks.

Jamie.