You must be experienced with Magento
You must be able to do install the script, do a design or a copy or another template, customize the cart.
Also you must be able to create a payment module for gspay.com.
Gspay currently does not have a module for magento, i can provide u a oscommerce or creloaded module and you need to convert it to magento.
If i am happy with your work on the first project then i will offer you work on 15 magento sites and give u ongoing work.
Please be reasonable on pricing as this project is long term.