I am independently developing an asp.net business application with a MySQL database. I currently have a Windows web hosting account which includes MySQL and MS SQL as installed supported options. I am not yet finally committed to using MySQL and I want to keep my options open to evaluate MS SQL and possibly other options such as PostGreSQL later when more of the business logic is in place - my data access layer will handle the database connectivity.

The web hosting setup I have now is fine for development purposes, but if in future I want to use, say, PostGreSQL Server, and a level of usage of, say, 10,000 hits per day concentrated in business hours, I'm assuming I'll need a dedicated server. But in that case, should I just install PostGreSQL on the dedicated server, or is best practice to have a separate database server - perhaps locked down so that it can only be accessed through the web server? And supposing it was only 2000 hits a day - how would that change things?

I'd appreciate it if anyone could point me in the direction of a useful guide to these sorts of issues. Naturally if I start paying for separate servers, I would like to know exactly why I'm doing it and what the performance issues and thresholds are.