Hello! first of all I must confess I am not a pro in opencart , I have just started for two weeks. But I have been working in web development for more than 2years now. I am familiar with MVC designs . My plan is to make a child theme of default theme or may be the whole theme if you wish with card based responsive layout. That page of your reference is not very mobile responsive they keep promoting to download the app, which is not a good practice always.
I am really keen to know what your specific requirements are.
I can make a lighter theme than the default one. Also it will be search engine friendly .
it will have all the opencart default functions of course.
Part of my deal is i'll show you whatever I make in live demo before you pay.
Looking forward to hear from you.
Thanks.
Add: Just finished an opencart project toady! Another one is going on!