Hey, I am an expert ASP.Net MVC developer with 8+ years of extensive experience in .net technologies. I also have an expertise in Javascript / JQuery which will be very helpful to implement your requirement of no-postbacks. For this I will use AJAX which I have been using since 7+ years now.
Please note that I have requested a 100% milestone, however I can update my bid in case you are not comfortable with this model. It would be great if you can propose your payment model and I can work on the same model.
Questions :
1. Which browsers you want your site to be compatible with?
2. What kind of performance you are looking at?
3. What database will be used in backend.
4. I hope you will provide the HTML/CSS for the site.
Answers to these questions do matter for implementation purpose however I dont have issues with any of your requirements and can start work as soon as you award the project.