No your not doomed by using tap water for a while, I started all of mine of tap water and then switched over to RO/DI after all of my learning mistakes were cured. If you don't have a RO/DI unit and have lug 5 gal jugs around from the water store, it will make this stage easier for you. A few "emergency" water changes could put you out of buisiness if you are lugging jugs around. I personaly would use the tap for a month or so until you get a hang of the whole thing and then switch over. You are going to have blooms as it is being a new tank, and yes there are Phospates and Silicates in tab water that cause algae, your not going to have an out break just because of that. While your cycling, reduce the photoperiod of light to keep algae at bay, get a cleanup crew, get fish when stablized, don't feed too much and you won't have an algae problem. When you got it all down and aren't changing water out like a madman because your alk is off or high amonia. Then switch over. You don't have to have everything at once......but eventually you should get away from tap