After your first grow, I might get something that you know what it is and what the potency and effects might be. You can order all over and cheap too. I have a pouch of seeds I collected over the years, some going back to the early 80’s even, just I didn’t use any as they are mixed so not sure what I would end up with.
Water, it just depends really. You can grow with tap water, I know many that do, it is just not optimal or you can spend hundreds on RO system which some say is best. I use distilled water right now, cheap easy to get, you can buy a countertop distiller for $60-$100.