Firstly, welcome to our little world :-)
My first thought is, do you really need a peg. In OpenToonz, you can apply movements, resizing, etc directly on each column.
However, if you want to use a peg to separate different movements, you can. But these aren't shown on the timeline, so you have to select the page name from the dropdown shown at the top left when you use the animate tool.
Personally, because the pegs aren't shown on the timeline, I like to create a dummy column. All you do is to create a new drawing level in a column (no need to draw in it or make it last more than 1 frame). Then parent that dummy column to your drawing column. You can then select this new dummy column to apply animation keys to. But again, unless you want to separate your keys or are using the plastic tool, which adds its own keys to the timeline, I'd just animate the columns directly when you can.
Regarding shrinking the canvas. Yes, you can resize any levels you already have, by right clicking on a drawing in the timeline and choosing "Canvas Size", then choosing your new size. However, if you need a different size, you're better off choosing that size when you start a new level. So instead of just drawing, click one of the New Level buttons at the top left of the timeline, or from the Level menu. There you'll be able to set your new size.
But if you want a smaller camera and level size, then you're better to set the option in File > Preferences: Drawing: New Levels Default to the Current Camera Size.
Then when you start a new scene and set your camera size there, afterwards, all of your levels will start at that size.
I hope that helps,
Good luck!
Darren