Help with advanced Wordpress development. More back-end than front-end.

I'm working on a client site. The current site has been live for 1 year and now I'm building in an advance section to the website which allows 2 sets of users to login, create a basic profile, list jobs / apply for jobs, send messages / read messages. I also need a 3rd admin user to see all activity by the first 2 users.

I've designed and built the front-end so I have a load of template pages that build up the 2 user journeys - login > create profile > add job > view job > apply for job > etc etc. What I need is for these front-end templates to start interacting with the back-end database. So when a user creates a profile, a profile is created in WP, when a user creates a job, the job is added to the database, and so on.

I run a small digital agency and my normal PHP dev is busy and I need to get this site finished ASAP.

I have a dev site up and running, wireframes, brief, front-end code.