I'd be more than happy to help you out on these:
- Can I set "A record" for sub domain? How? Is it free of charge? - yes, for free!
- How long to setup the hosting after sign up the service? - most new accounts are setup within 24 hours
- Can I use ASP.NET 3.5? If no, when will you upgrade? - yes, just e-mail email@example.com if you need it enabled.
- What is Coupon Code? Is it discount code? - that is where you would put a coupon, if you have one.
- Do you have MySQL Database, PHP, SSI in "Windows VPS"? MySQL, SSI* and PHP are supported.
- Can I use the same dedicated IP if I upgrade from "Windows Hosting" to "Windows VPS"? - no, sense dedicated IPs are assigned to the server you would probably need to get a new one.
* With SSI do you mean server side includes? If so it should be supported for Windows VPS.
Hope that helps!