Is it possible to assign the drawing tools / fill styles which I commonly use to custom menu buttons? How much work would be involved?
You should be able to assign the command
DRAWTOOLSM drawtool name;
to a menu button.
FSTYLE fill style name;
should set the current fill style.
See this article about menu editing for doing the actual menu changes.
Do note that menus aren't style sensitive, so the buttons would only work properly as long as the current style actually have a tool/fill by that name