You can add the applet Accessibility to the panel. It has some nice options...
To change the menu font, you need some editing in cinnamon.css.
Is your theme installed by default, or did you install it yourself?
If it's pre-installed:
1. Run Gedit as root. Open a terminal and type "gksu gedit", then type in your password when asked.
2. From the File menu, choose Open, then navigate to File System/usr/share/themes/YourThemeName/cinnamon/cinnamon.css. Open it.
3. Scroll up to the beginning of the file. You will see something similar to this: "font-size: <number>px". Change the number to the font size you want, then save it. DONE!
Note that this is just for the menu text and taskbar text, other elements (tooltip etc.) won't change...