Need MAGENTO Expert for Shopping Cart Testing and Fix

We have a Magento website running ver. 1.9.0.1. There are 4 issues we need you to fix. 1. MOST IMPORTANT! Several customers have complained that all their information disappears during checkout, or that they are not able to enter their credit card information. We need you to identify the problem with the checkout process. I have tested the website on the latest PC versions of Chrome, Firefox, IE11, and Safari, and all were successful. I have NOT been able to reproduce the issue myself. If you can obtain the information about the checkout failure from the server logs, that is great. If you would like to implement the checkout behavior feature of Google Analytics, you are welcome to do so. But we NEED you to definitively identify the recurring checkout problem and fix it permanently. We have experienced this issue in past versions of Magento and had it fixed, but it has come back. 2. Some customers complain that they cannot upload their artwork. We need you to identify the problem and fix it. 3. When I use the password reset function, I receive this error message. We need you to fix that broken function. Fatal error: Call to a member function setCustomerId() on a non-object in /home2/____________/public_html/app/code/core/Mage/Customer/controllers/[login to view URL] on line 763 4. When I was testing the website in Safari (for PC), I got an error message after I logged in on the front end of the website as a customer. Please see the attached screenshot. We need you to fix this error. Issue #1 is CRITICAL and we absolutely must find a solution right away. Please do not bid unless you are sure you can figure out what's wrong and fix it permanently. This is a confidential, third-party project. You may not contact our client or use this work in a portfolio or advertising of any kind. If this sounds amenable to you, we look forward to working with you.