Windows 8. All programs open in a small window. How do I vary the size of this window or, alternatively, have the new window automatically open full size?

1. Have you started facing this issue recently?
2. Are you facing this issue only with shortcut folder or programs?
I would suggest you to follow these steps and check if it helps.
a.Close all windows except one of these smaller windows.
b.Grab the corners of the small window with your cursor and stretch it to the desired size (do not use the maximize button on top bar).
c. Now, close the resized window.
d.Now, open the window, the resized window will be the last window closed in order for its size to be remembered.
If you are facing this issue on a shorcut folder or programs, you have the option of always opening the windows in Maximized mode.
a. Right-click on the shortcut program and choose Properties.
b. Under Shorcut tab, choose Maximized drop down menu next to run.
c. Click on Apply and OK.