Here's how I do it: After completing the first loop, I straighten and tension the two bundles with the first loop hooked over something. Then, I make my back twists the SAME direction as I make my twist for making the cordage - not the opposite direction. This works out because once I have made the correct number of twists for the second loop, I fold the string back and blend in the tag ends. Now I am twisting the string between the loops the same way as before but have reversed the string as I twist and cord in the tag ends thus unwinding my pre twists. I find about 25 twists is correct for me.
Clear as mud? Try it and you will find it works.
I twist the strands by rolling between my thumb and finger away (the top of the bundle away or clockwise if you are looking at the loose end and are right handed) and folding the bundle up and towards me. Then I move my left hand grip up a smidge to hold this twist and do the same with the other bundle.
If you do it prefect it will end up with flat untwisted strands between the loops. There will be some twist of the bundles between the loops the wrong way that will unwind and then wind the correct way as you twist the whole string in the direction the cordage lays near the loops.
String length can be done without a jig by making one loop and putting it over the nock of the bow. Stretch your bundles towards the other end and do the pre twisting as described. Now pinch the two bundles about an inch longer than you want the string (you are going to loose some length when you cord the tag ends in ~ one inch). When you cut your bundles, make them about 18 inches longer than the bow. Offset or trim the first loop ends staggered so they blend in after making the loop. When you make the second loop you can just start dropping strands after a couple inches of tag end blending. Leave them hanging out and trim after the string is done.
For a recurve I like to make my string end up about 4 inches shorter than nock to nock (AMO). 58" AMO would be a 52" actual finished string length.
It takes some practice to make the string look as nice as the pros, but you'll get there.