We use Campden (or the purer potassium metabisulfite or sodium metabisulfite salts). Initially, we use it to kill off any potentially harmful bacteria that may have hopped a ride in with the base ingredients we use in wine making, and to discourage any wild yeast from gaining a foothold. Campden will not kill yeast, but it creates an environment inhospitable to them. As SO2 released into the must and atmosphere above the must dissipates, the environment slowly changes and the yeast can grow, but by then our cultured wine yeasts, which are more tolerant of SO2, have gotten a good start and "crowd out" the wild yeasts, use up all the dissolved oxygen, and consume all the fermentable sugar and nutrients. In the end, there is nothing left for the wild yeasts and they die without propagating. Adding campden tablets helps stop a wild yeast but a good yeast starter will do that. If adding it a day before you pitch your yeast makes you more comfortable, by all means do it. You won't hurt anything.
No need to heat the juice. Boiling the must will give you pectic haze. Pectin is a complex sugar found in the cell walls of all fruits. This substance is what causes jams and jellies to thicken and has many other uses in the culinary arts. When wines are made from fresh fruit, pectin plays a valuable role in making sure that optimal flavor is extracted. However, if the pectin in the beverage is not properly eliminated during fermentation, the wine can develop a hazy or cloudy appearance as a result of the excess pectin being held in suspension in the fermented liquid.