After boiling my wort, it it ok to add ice cubes to it to not only help cool it down but to help add to the water volume needed to get up to 5 gallons? I haven't done it but it certainly has crossed my mind.
Part of the reason for the boil is to 'cook off' anything that might be in your water. If you're using bagged ice, the assumption is, you don't know where that water is from.
But, there is nothing to say that you couldn't boil, then freeze water ahead of time of your boil.
Yes, but you want to make sure the water is sanitized. So, use distilled water, or at least boiled water, and freeze it in sanitized, closed containers and not just regular ice cubes from your freezer.