Dependencies for LaunchAgent so it mounts a bundle before other daemons run
Firstly, a rant: Sparse Bundles work in a way to allow the bundle to increase in size to accomidate it's contents, however any files that you modify or delete in the bundle will not decrease the bundle size as you'd expect. For example, if I add two 1GB files to the bundle and then delete one, the bundle will be 2GB in size. If I then add another 1GB file, then the bundle will increase to 3GB in size. Long story short, don't run applications in bundles.

As for the LaunchAgent for Steam, it's probably just a background server connection. I would disable it within the Steam preferences if you can, and/or try to remove it from the start-up list.

There is no built in delay for startup apps that I'm aware of.
I use Keyboard Maestro for this. My workflow is for Keyboard Maestro to launch at login, then to wait for a certain period of time (delay) after login and then launch an app (eg Dropbox).