Different bows come in Half Lengths... Mathews come in Halfs... Mine is 27.5... Also which release you choose will effect your draw length as well as if you shoot with a loop on the string...

Yes your arrows will be directly related to your draw length and if you have an overdraw or not...

Far as length of bows, the longer it is the more "Forgiving" or easy it's supposed to be to shoot... But Most of todays new bows are Forgiving anyway (your brace height will have effects on that as well)

There are TONS of things to consider when getting into a Bow, and it's best to goto a Real Pro Shop and get opinions and have them help you with the proper setup for you... If Possible goto more then 1 shop and get an education from them... They will be able to get you setup properly and that's more then Half the Game...

Good Luck...