See if you can download the owners manual from Beneteau if you don't already have it. When I got my 323, the dealer gave me a three ring binder with all that in it. There is a section there which has a table of all the line sizes and lengths for the boat.
I do know that my reef lines are 3/8" ( or about 10mm) which is probably a bit on the heavy side. I am guessing on my boat the #1 reef is 75 feet and that leaves a lot of extra in the cockpit, and the # 2 reef is close to 100 feet. Yours may be a little longer.
A good estimate for each line would be to measure the distance from the reef point to the foot of the sail at the tack end and double it, likewise for the clew end and double it, add them together, add the length of the boom, the height of the boom from the cabin top, the distance from the mast to the cabin top winch, and another 10 feet or so.