I am going to also add a +/- button.

So when you click on the Hand button, there will be a "new" toolbar where the buttons on the right of the hand would become:

+ Add page after the current
- Delete current page
-> Goto next page
<- Goto prev page
<dunno the icon yet> Goto page #

(in Hand mode there will be no Undo/Redo/Share/Color button)

If you feel you need more options in this mode, I may switch to a toolbar with something like:

< Back button
+ Add page after the current
- Delete current page
-> Goto next page
<- Goto prev page
<dunno the icon yet> Goto page #
and there's space for whatever you may think useful in this mode among:

New page before
New page after
New page at end

Also I am trying to figure out how to show a vertical bar of icons. Once I figure this out you will be able to tap on the Pen as usual and start drawing, tap on the Pen again and this vertical bar of icons will appear to select, for example, Pen thickness or Draw straight lines.

Same for possible other icons that may have several options associated with them (like the Eraser)

Now that I think about it, this way I can "fix" the Color button as well. First tap would show this vertical bar with a few selected colors + an icon to show the Color Selector... like that.
Or would it make the Color Selector too far away ?