When I was designing the $50 robot I first decided to use DC motors because its cheaper that way. But the problem with them, as you are quickly learning, is that they require gearing and control electronics - each complicating it for a beginner. Using the servos will save you between 5 and 10 hours of work for a cost of about $3-$4. You need to buy/make a motor driver
As for the IR sensors, that replacement should be decently easy. I perfer the photoresistors for beginners though because they are easier to test with - the human eye can see the same light the photoresistor can.
because i took them out of a toy i dont know the voltage, operating current, or the stall current
Hook it up to a power supply or multimeter and run some tests on your motor. Chances are you have an 'el-cheapo' motor, meaning it will work at about 6V optimal.
As for the gearing, this has been mentioned many times in the forum. The gist is that homemade gearing systems are not worth the effort. You need a motor that already has this built in, such as a servo