A good way to start is taking a font that has fixed kerning (such as courier), this will also fit your typewriter look you wish to achieve.
Then use two text layers:
1) The actual text
2) use a block character from a dingbats font (I have used Marlett and the letter ‘g’) that will have the exact structure of the actual text (each block will cover one character from the actual text)
now use an animator per layer, one will reveal the text, and the other will show the block character, only one at a time.
here’s a lousy version of what I mean.
Contact me if you need further help
Regards,
Elad