The help section of the Harmony software is pretty good, but only if you know what question to ask.
Failing that, googling a specific topic will probably give you some answers.

To start your "TV" activity on a specific channel, you can add extra commands. Run through the setup procedure for the activity, and answer one of the questions with "everything is working, but I want more control" (or something similar), and you get to a screen where you can add more commands to the start and finish of an activity.
Add the TV codes for the channel you want.
Many devices also allow you to switch them to a specific channel or input when they are first powered on. Again, the setup procedure for the activity will ask you the relevant question.

Not sure how you could set the volume of the receiver to a specific number, though, unless your receiver supports direct level setting from the original remote.

Basically, anything you can do by pressing buttons on the original remote can be done from the Harmony, either by pressing buttons, or by adding multiple buttons to a single button or an activity.