to touch drag on one axis: simply take in account the vertical axis and that's all, as you are processing touch position only get the y component and you are done
To limit max drag, if the vertical position if below a certain value, do not process the movement, but still watch for the the touch and as soon as it's above the value again, move again.
to pitch and calculate percent would be using the same base. You need to know the start and end valus on screen. and to compute the percent ( ranging from 0 to 100) you would do the following:
total travel = max - min
current travel = touch position - min
percent = current travel *100 / total travel
once you have the percent you adjust the pitch using that percent value. note that you will have to choose a range for your pitch min and max and apply the drag percent to that range and set the pitch with that result.
Hope it all make sense
You'll be fine, because you have already cut down the problem in digestable chunck. so really take them step one at a time. and don't hesitate to ask for more if you get stuck.