Hello! I am a web developer with extensive experience in PHP,HTML,CSS,JavaScript. I have made couple of WordPress themes and few plugins as well. That site of your reference is running on a custom cms, definitely not on WordPress. I would suggest you not to go for a custom Cms, because not only it may have massive security flaw but also it will not be as extensible as WordPress. Like the buy/sell option you are looking for, woocommerce which is a WordPress plugin does exactly that job, it is the most popular e commerce platform today.
So all you need is to install WordPress and woocommerce and choose a proper theme of your choice. Now it is unlikely to get same kind of theme as that site, what I can do is make you similar looking theme. Or I can help you setting up your site on other themes.
Other process of making a site involves domain name,hosting , SSL, Google analytics, Google indexing
I can take care all of these also i offer two months maintenance
Let me know if you are interested, we can discuss more over chat!