Magento Based e-commerce website build

We are currently looking at the option of a new e-commerce website to be based on Magento platform. We currently have an opencart website that is nearly two years old which we were originally going to update, but for us to go forward with live stock feeds we require a magento site so the plug in from our feed supplier (this will also enable us to get all product data/images etc) can work, and also we will require the m2e pro plug-in to enable quick listing onto Amazon/Ebay from our new site. Out current site is [login to view URL] , please have a look as this will give you an idea of what we are looking for. Ignore the sreen resolution as we had to reduce the size so it could be embedded into our facebook page, this is not something important we require. Our exisitng site is enabled to take payments via worldpay and paypal, this would require set up. Also their is alternate product delivery options (some products are priced including delivery, some are not with a minimum spend threshold to enable free delivery). We are looking to for a quick turnaround should we decide to progress with this project, so please can you supply how long before the site would be fully operational. Also we will be looking to transfer the domain name form the existing site to the new site, We will choose/purchase the theme layout for the site from somewhere such as templemonster. Please feel free to ask any questions. Thank you for reading