Additional patches to php sql POS script

I have an existing POS script initially designed by a freelancer and just last month fixes made to some issues left by the initial freelancer. Now i'm after some more patches to make the system even better. My point-of-sale (POS) system is served from my website (which is a paid server). It is programmed in php, mysql, html, ajax, javascript & css. I use Google Chrome (IE and my pos script has issues) What I now require is for the following: 1-a notes section added to the invoice screen so when an invoice is made I can add notes like add a serial # which then displays on the invoice (and saves this information in the invoices table. 2-i've added a 'trading name' in the customer database, but require it to be searchable when i search the customer database on the invoice screen and display accordingly on the invoice. 3-sometimes the ajax dropdown box used when I start typing in the product number remains on the page, need to have a fix so either i press escape or click a little X or something. 4-Add a part-payment input box to the invoice screen, so if a customer pays me a deposit, I can enter this amount in. (as the invoice currently has 'outstanding balance' for that customer). 5-Total Tendered field to be added to the invoice screen (as I frequently catch my wife using a calculator if the customer gives her more than the invoice amount) :) 6-On the expense screen, if I enter a negative amount (so I get a refund for an expense i've purchased), this amount displays on the list but doesn't calculate properly on the profit & loss and GST screens which puts my totals out :( I was initially quotes $80 for points 1 & 2, but as there is 4 other points, I expect it to be more. I would like this to be completed within the 2 weeks if possible. I will make milestone payments on the way for each point you create and send to me, with the final payment when I have received the last point and test it. It is imperative that this is a currently live system, so I can't have issues of a script going haywire and causing totals to be incorrect. I can detail more information if required and can send you the current scripts, but please respect the privacy of all information contained like customer details, supplier details etc.