2.x refers to post-2.0 trunk.

Mono has a patched Boehm GC included (libgc) and an embedded version of GLib (eglib).

libgdiplus is only required as runtime for the System.Drawing assembly.

Bootstrapping does not strictly require an existing Mono installation. The official way to bootstrap is to use a released source tarball. For trunk you can obtain an unsupported snapshot of core assemblies, referred to as monolite. This works only if the version of monolite matches that of your working copy, i.e. SVN trunk HEAD.