if i use a speed controller and a motor, can that basically take the place of a servo?
Well, it can take the place of a modified servo for continuous rotation. But the DC motor has to be driven by a H bridge driver, and the use of PWM can controll speed.
With a servo you can calculate the traveled distance. The servo works in pulses that you need to generate every 15 to 20 milliseconds so the servo will rotate continuously. Depending on the wheel diameter, the robot will travel a certain distance for one pulse. If you measure that, you will be able to calculate how many pulses will be necessary for the robot to travel a certain distance.
You can do the same thing with stepper motors.
To do the same thing with a DC motor you need wheel encoders.