Build a client data/reservatiion/billing/reporting system.

I have a dog walking/training services company, with an up and running website for information only, no existing software. I would like to build an online system, where the client can sign up, fill out his details, the dog details etc, the data will be saved in our database for future use. In order to sign up, a client will have to approve terms and conditions etc. Upon login, a client will be able to book the different services out of the "menu" (on a calendar) with his assigned walker, or if the walker is not available for that specific time frame, it will automatically divert it to his backup walker, while notifying both the client and the walkers. At the end of each billing cycle (biweekly), the system will create an invoice for the client and email it to them, then it will either automatically charge credit card within 3 business days, or it will send me the invoice and I will charge it manually. The system will also report every billing cycle the amount of jobs each worker did, and create his paycheck, notifying both the walker and the manager of the amount. Reporting will also be needed monthly/yearly upon request, per client/walker/totals etc. All clients, billing, and paychecks data will be saved in the system for future use. Also might be needed is a shopping system for dog related products I'm about to offer for sale in the future. With a shopping cart and the works. Will use paypal website payments pro for all credit card processing, so might need something to integrate with that.