Adding Paypal API Features to my site

I run a site where business clients can send SMS to their employees. This already works fine. However, I want you to add some Paypal features (see below for details). ## Deliverables Using my system business clients can run SMS surveys. If a survey is executed, random employees associated to this account receive a SMS to attend this survey. I want you to add the following features: 1) As each account has its balance, a certain amount of money (e.g. $sms_costs which should be defined in the source code) should be debited from the account each time a SMS is sent. So if a survey is executed and causes 10 SMS to be sent, this should debit 10x$sms_costs from the account of the business client initiating the survey. 2) Business clients should be able to charge money to their account (a form to enter the amount, redirection to pay with paypal, payment, redirection back to my site should be suitable here). After payment is received amount has to be charged to the specific account and I should receive eMail-notification. 3) My website should show kind of a warning message that the business client is not able to perform any more surveys if the account amount is below $number_of_surveys_*$sms_costs*$number_of_employees associated with this user. And that he should charge money to his account before. Of course if he still wants to initiate surveys without having enough money on his account, this warning message should be repeated and no SMS should be sent. I will show you more details regarding the layout after selecting you to work on this project. Of course you will also get FTP and MySQL-Access to my server to implement these features.