This all sounds like something you don't want to do as it will eventually mess up a decent tape recorder. The only way I've found to do what you are talking about will take 2 different recorders with mics (built in or not), and two or more tapes. This is the way I used to do it, but keep in mind, eventually, there will be a degradation in the recording quality.
I would record my first track straight to my recorder, play it back and listen for levels, mistakes, etc. Then I would set up a second recorder with a blank tape, my amp and the first recorder in an X,Y pattern, hit record on the second player, play the first one, and play my "second" track along with it.
This method is tedious and if you make a mistake.... you know. Your best bet is to invest in a decent 4 track. They are getting cheaper all the time as digital takes over the market.