we have a bunch of sample applications which we run nightly integration tests against. As for application tutorials themselves, we have the buildpack[1] and the dockerfile[2] workflows.

[1]: http://docs.deis.io/en/latest/using_deis/using-buildpacks/

[2]: http://docs.deis.io/en/latest/using_deis/using-dockerfiles/

I can't give you an answer on how many apps you can run on a 3x2GB cluster. It really depends on how much memory/clock cycles your apps require.