I am planning on attempting to design an overdrive pedal soon. This will be my first attempt at designing a pedal. I have built several circuits (most not guitar stuff) at school (including a fuzz) and work so I feel that I have enough experience/technological know-how stuff to attempt this.
Anyway, I have a couple of questions that I feel are important to me having any sort of success in this.

1. What is the maximum voltage that should ever come out of a pedal? I don't want to accidentally do something too high that could damage my precious tube amp. I looked in the manual to see if it listed a maximum input but didn't see anything.
2. What sort of output impedance is typically good? I did some reading on the tubescreamer and saw that between most models it was between 5kohms-10kohms.
3. Higher input voltage makes the tubes clip more, right? (Just want to verify that I'm not an idiot. If I'm wrong, feel free to tell me that I'm an idiot.)

1. Different pedals have different voltages, I'm not sure if there's a set "maximum", but remember, the voltage from the output will not be higher than the power supply to the pedal.

3. Yep. The bigger the waveform from higher voltage means that more will be clipped by the tubes.

Can't help much with 2, sorry!