Bobo96, I have the same stringer as you and here's how I do it.
First, beware of the "tower creep" problem - that's where the 12 o'clock and 6 o'clock mounts will creep inwards. I solved the problem by putting a piece of leather between the tower and the base to increase friction.
Second, buy a starting clamp. Makes life much easier. First, put the starting clamp on one mains, then (fix) clamp that same main. So - you have both a clamp and the starting clamp holding it. Just make sure the fixed clamp doesn't sag down - might have someone hold it in place. Next, pull tension on the other mains, and keep going until you string 3 mains. Now go back to the main with the starting clamp, pull tension on it and string 5 mains, etc....
I've done >50 frames this way and no problems at all.