Client Portal For Website

Hi, I run a business called Bookkeeping Central. [login to view URL] <http://www.bookkeepingcentral.com.au/> I would like to add to my website a client log in where clients can enter the basic information for Invoicing, quotes, banking information (like cheques deposited or spent etc). Possible somewhere they can upload their latest bank statement, I have attached links to a current form we have. The ability for us to tailor the forms would be fantastic. [login to view URL];hl=en That form in for invoicing, we need one similar for quotes, check deposits and withdrawals. So four in all. While I will consider a generic form initially, ideally I would like to taylor each form (mostly the invoicing and quote form to out clients requirement.) So an administrator fuction were input fields can be added and removed would be perfect. Happy for it to work in an iframe. I currently use googledocs to do this but I want a more secure option and professional looking option. If you know how good dos works, that would be the idea interface for me.