if they are completely submerged the will not get the oxygen the need. leave a gap. they will grow into the water. the area that is left out is drying and getting O2.
an actual outdoor plant that is in the ground will not suffer from extreme temperatures. the roots will never reach that temp, if it is in a pot and not in the ground it will slow growth a bunch.
I don't think you have to worry about people not respecting you. You are doing a fine job of taking care of that on your own. He is correct you are posting spam.
Also, you didn't spell that correctly..."dident".....lol
Again even with a 600 it depends how tall you let them get in veg as to if you need any side lighting. Look into a digital dimmable ballast. That way you can possibly use it for veg and flowering and just have some different options. It will run both bulbs MH & HPS.