BCY-X is my current favorite string material, but Dynaflight '97, 452X, 8125G, 8190, etc. are also good. For serving, 62XS or Halo. I only use BCY products. After around 20 years of making and studying strings, I think they have the best product and (based on my experience) they have the best customer service.
18-20 strands of X makes a fairly small diameter string (it's a very small strand) that remains durable with very little stretch/creep.
I like the loops padded to 24 with B-55. With this strand count, you can use .025 62XS to get a good fit with GT nocks, and won't have to do anything extra.
If you get the DVD "How to Build a Great Bowstring", I will be happy to answer any questions you might have about it.
Good luck!
Chad