Making a Dock app and want to know what is possible.

Nice! It's great that you can make something usable even with a few bits of tape :)

3) Move widgets to the left-hand side of the screen (now top in the dock). - I am not sure how to do this one? Is there a universal value for the widget bar that can be changed by other apps?

WIDGETS.forEach(w=>w.area="tl");Bangle.drawWidgets(); should do it :)

4) have notifications pop up on this repositioned widget bar

Should be ok - you'd need to make your own notify module for this but you could check out the existing notify/notifyfs for examples.

5) Power saving -I know it will be on change anyway but was thinking of having a setting for times when the led brightness is lowered to 0.2, i.e. during the middle of the night

This is something that there's an issue open for already, so it might get made a separate app at some point - but it'd be pretty easy to add something to your dock app.