Control System 4 with just a keyboard?

Solution 1:

While it is reasonably possible to use a classic Mac without a keyboard, using one without a mouse requires a System software disk with the Easy Access control panel installed.

With Easy Access installed, you can press Command-Shift-Clear to toggle Mouse Keys at which point your numeric keypad can be used to control the mouse cursor and the computer will be frustrating, but functional.

A limited number of shortcuts are still documented on Apple's site in Archived Technical Note 28141. Also, you can select icons in open windows by typing the first letters of the icon's name (for example, 'sys' will select "System Folder"), followed by Command-O to open.

Solution 2:

As far as I know, there aren't enough keyboard shortcuts (apart from your copy and paste, etc.) that'd allow you to play with the OS too much. I also couldn't find a reference - things like this are surprisingly scarce.

I did find a Macintosh ADB mouse from here though - if you're alright with eBay or things like that.