Changes to a quote script - integration into website

We already have the website and quote tool/buyback script. We have a wordpress site and an electronics buyback script, however, the seller of the buyback script is not able to add customisations we need. Firstly (2 options) we need the header of the buyback script to look exactly the same as the wordpress site, so the user does not realise they have went to a different page. I'm not sure how easy this will be as you will have access to the sites header files so maybe a copy and paste process but as it's a wordpress site so i'm not sure. OR, remove the header of the script completely and use a responsive Iframe so the script is on the website page? It's up to you and whatever you think will work best. Secondly, the end of the quote tool has a form where the user fills out collection information, I need a few changes in this form, i need a checkbox added, a few of the label names changed etc. Thirdly, the script has options which we can see in the back end, such as processor, hard drive etc. we need a new option added called 'faults', again, maybe a copy and paste process and link it with the database. The last thing, which the seller of the script is trying to do for me, but possibly would get someone else to do it if they can do it quickly, is the script displays the prices with the dollar symbol, i need this changed to a pound symbol. There will be more changes in the future and we would like to work with an experienced professional we can rely on to make customisations quickly and effectively. Thanks