I'm working at a site similar to Foursquare and Yelp, with approximately 100000 unique requests each week that generates content, growing steadily. We are currently using:

• Seam as Java web framework.
• MySQL as DB
• Hibernate as ORM
• Hibernate Search as Index
• EhCache for Caching.

Since our site is slowly growing out of the current setup and has a lot of legacy code, it is time for us to start thinking about a major refactoring/changing setup.

1. Web framework

   We are not ready to change the language but we are leaning towards Spring Web Framework, since:

   • Seam is no more.
   • Almost all of us have worked with Spring and liked it.

2. DB and ORM

   We have done a little research and we are thinking about MongoDB.

3. Index

   Do we need to have a separate Index if we use MongoDB?

4. Cache

   ?

So my question is basically:

If you take Spring Web Framework and MongoDB into consideration, how would a good setup be for a web application that is growing and handles a lot of logged in users generating input and performing searches?