HI there! So many questions and no pictures to help me. If you tile the entire wall behind your vanity, there is no need for a splash. I tend to tile the entire wall so that mirrors, etc. don't have to cross over a tile-to-painted wall condition. Also, doing entire walls in tile eliminate the up/down/up/down tile as it goes from the shower/bath (up) and then down to the wainscot (down) and then maybe down to the floor. And yes...terminate your tile ALWAYS ALWAYS ALWAYS with a bull-nose (if thin-set) or a quarter-round piece (if mud-set). Good luck!