Mobile development

I need a responsive website. I would like it designed and built. I own a small staffing agency. We recruit, vet and supply casual staff for events and festivals. I need a system that can creat a user portal to apply for vacancies, submit timesheets and book staff. I'm not looking for anything complex, it must be user friendly. Its purpose is to streamline our back office processes to save time in administrating the business. I need a system that can be built upon so it can grow with the business. Staff must be able to register, create an account, complete registration documents and submit attachements. They will need to submit weekly/monthly timesheets and monitor its approval status and check their historical pay records. They will also need to be able to update their information, such as a change of address, telephone number or bank [login to view URL] are employed and self employed, so the timesheets must reflect this for compliance. We will also need to use the system to book staff, will will send a broadcast message by email/private message with details of a job that they can accept or reject. Once accepted it will automatically populate the booking order and send them a confirmation message with further information. On the back of the system we will need to produce reports so we can integrate the data with our accounting sustem Xero for invoicing and payroll. I would like to build more into the system, but this is the core requirements