You can aerate before or after you pitch the yeast, I do before I pitch. You can use regular tap water as long as you think it tastes ok. If it tastes ok it should be ok for your brew. If you do full boils then using tap water is fine. If you are concerned about chlorine, Chlorine is boiled out of water in about 20 minutes, unless your in an area that now uses chloramine, which cannon be extracted from water.