help making this software : little tired cant think strait

i have this paid service running online many users make online request i carry out there request then get paid now , i wish to make things more smooth easy fast as possible to handle many customers same time


what i need a tool that can

add username
request info
$ payment info how much has been paid and owed
and save the data.

after request has been completed by our staff we need to inform user he needs to pay remaining amount owed.

i will off course make a client and server so i can send and retrieve data.

i got some ideas just thought il make this post and get some more ideas out of you:pplz