Unvacuumed gravel serves very nicely as a nitrate reservoir, so if the tank is unplanted, gravel vacuuming util you get the nitrate back under control is a good thing, followed by routine vacuuming once you are restabilized.
Just use the vacuum cleaner for draining the water and vacuum whenever you do the water changes. No reason not to. You don't have to vacuum the whole tank with a single water change. Just be sure to move around from one cleaning to the next.
RTR did a great job explaining what I meant about Nitrogen. Aging your water will take care of the dissolved gas issue allowing large water changes. Even if you let the water sit only for an hour or so though I would reccommend 24 hours, you will get some degassing which are those tiny bubbles you see.