Hello, we just completed very similar project - an upgrade of the existing website into new and modern look.
We used latest Joomla for that task, take a look our last works http://www.freelancer.com/u/cdesigneu.html
All templates are modern, clean, CSS3, responsive (mobile-friendly), seo optimized, customizable (changing of colors, fonts, module positions).
We can install desired theme at our demo server, so you can apply the customization. After the website is completed, we will migrate it to your domain.
Ready to work on daily basics! We are dedicated to quality work, 100% completion rate, 5 star average rating team.