You don't need to boil the water first, unless you're on well water or something and it's terrible quality or is high in fluoride (in which case you can use low fluoride bottled water, distilled water, or nursery water). You definitely don't want to boil the water with the powder mixed in it, because heating formula then cooling it then heating again can cause bacteria to grow.
If your normal tap water is fine or you use bottled water, just mix formula at room temp as needed. You don't have to heat bottles, unless your baby is just particularly fussy about it. Whatever is left in the bottle after baby is done, discard immediately. If you want to prepare bottles ahead of time for convenience (ie, someone else is watching your baby) then use room temp water and put the bottles in the fridge OR buy premixed formula. Your baby might take a bottle from the fridge cold, but if you have a picky baby then you can heat bottles up. Once you mix a bottle or remove prepped bottles from the fridge, use within 1 hour.