Its difficult to tell you exactly the length you need. I do t see string grooves cut yet so measure the nock to nock length once you cut in your string grooves. Have you tillered the bow yet? If you have then use you tillering string to get better idea for more accurate measurement of the length of your bow string. A basic rule of thumb would be the nock to nock length minus 4”. Before doing that though I would use a tillering string to get you limbs balanced up and bending the same. After that I would make a string or order one from online that puts you around 6.5” brace height or just under 7”. This will give you less wrist slap when shooting the bow. Looking forward to seeing it strung up! Use larger loops so that the string loops straddle the siyahs or levers. I make mine so that the heels where the siyahs meet the limbs are about 1/2” gap from the string if that makes sense. If you do t then a string bridge may be an option too. Best of luck. Keep it up