I’ve seen some teams that start breaking into multiple projects from the beginning and others build behemoth single projects. The large project teams say that one massive project is easier to maintain than multiple smaller projects.
In general, how many files is too many?
The answer as George suggested it depends…but you may have large project with many areas which are new feature with asp.net mvc 2.0 . The time when you do want to break it another project is when you are trying to reuse that in another project. Since you do not want something coupled that it needs quite a few changes to work.
So, you need to analyze and understand the reusability of your projects.Ideally you would not want to have one big project with everything…you can divide into libraries..helpers..Models..etc..But again depends on how and what are you implementing..and sometimes a one large project also works.