It can get a little costly but I've found it often times takes some trial and error to zero in on what length string to order from a particular string maker with a particular type of string material. I like having as few twists in the string as possible - I will know what brace height is best for tune on each of my bows (write it down or tape on lower limb of bow) I take the strung bow and check its brace height and tweak it to proper brace if needed, I then take the string off the bow being carefull not to let it untwist and stretch it taunt between two pegs on my work bench. Then I measure the string from the end of one loop to the other. Once I have this measuremnet I will substract anywhere from a 1/2" to over an 1" depending on whether I'm using B50, Ultracam, D10...etc. This is the number I give the stringmaker. When I put on the new string it will usually settle/stretch in the first few days (I keep most of my bows strung all the time)and then I only need very small twist adjustments to get to perfect brace. I've had experiences where a new string stretched so much that it took a crazy amount of twists to get the bow to proper brace, making it look like a tightly wound barber pole and sometimes making the string kinky when not under tension. Strings with excessive amounts of twist to keep brace are not good, those strings should have been ordered/made shorter/better to begin with.
Like I said, this can get expensive if you start experimenting with new string materials and/or stringmakers. Over time I have settled on one stringmaker that I really like with a string material I also like, I know exactly what length string to order from him for all my bows. Once the intial stretch takes place, brace height is usually very close or requires just a few twists.
Keep in mind if you decide to go with one of the very low strand count "skinny" strings that it takes a lot of twists to make fairly small adjustments in string length. There just isn't enough diameter to take up much length per twist. It is even more critical to get these strings to settle in very close to your brace to avoid excessive twisting. As McDave pointed out, some strings seem to never settle in. I once had a skinny string ordered for one of my 60" recurves, I subtracted enough length when I ordered to where I figured it would settle in close to my brace, but it kept stretching so much that I could not get enough twists in it without making it a kinky mess. So, I took the string untwisted it as far as I dared and put it on one of my 62" recurves. Brace on the 62" was quite high to begin with, but it eventually stretched too low! - I twisted it up a little to get to brace and it has finally stayed put. That is a LOT! of stretch. I ended up retiring that string, because I didn't trust its construction. I've since settled on a different string maker who also makes low strand count strings and have not had that issue again.