help: 16v batts and HO alt

first time messing with 16v stuff. first of all if i get a HO alt that charges at 18v will that mess with the rest of my cars electrical? Can i run 12v batts off of a alt that charges at 18v? what are some good cheap 16v batteries? how many AH of 16v batts would i need for a 6k set up? what company of HO alts should i go with? sorry for 20Q's just lookin to learn //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif