I will answer that with a picture.
Depending on the initial scale of the map, you will be able to zoom out more or less. If the initial scale is huge, then you can zoom out more and still be legible. If the initial scale is small, then if you zoomed out very far, it might not be so legible.
To zoom out, either go to the “View” menu, then select “Zoom”. Or hold down ALT and scroll your mouse wheel.
And yes, you can do actions while zoomed out. You can do everything while zoomed out that you can while in the default view, including moving units, purchasing, etc, everything.
Here are two screenshots:
50% zoom of A&A 50th Anniversary Edition:

100% zoom (normal) of A&A 50th Anniversary Edition:

thx,
veqryn