To get special characters you were looking for:
Option-g copyright
Option-r registration
Option-2 trademark
Make sure you hold the option key down first before hitting the other key.
If you look in KeyCaps (should come with your Mac) under the Apple Menu, open it, select a font and you will see a small keyboard onscreen. Look at it, then hold the option key down and you will see more characters. Then hold shift, and combinations of option/shift,command, control. Each font has its own characters but many are the same in all fonts. If you use KeyCaps, you can hit a key and it will show up on a line above the keyboard. You can then copy this and paste it in your document. You may have to apply the font to it in your document. However, for the usual ones, as you were looking for, eventually you easily memorize them and don't have to use KeyCaps too often.
Fractions are a bit more time consuming. For the first number(s) of the fraction you type it as a Superior character (last item on the bottom of the Measurements palette. For the slash you can use a keyboard slash, but the correct fraction slash is Option-Shift-1. Then the for the second number(s) you type it in Superior AND Subscript (last 2 items on the Measurements palette).
I've never tried the extension mentioned so have no comment on that. If you use a lot of fractions, it might be something to look into. Hope this helps.