Sanitizing your fermenter is a good idea. This helps to remove anything that might interact with your must. However, the must itself does not need to be sanitized. In fact, trying to sanitize the must will probably result in a very slow fermentation because the sanitization will also carry over and affect your yeast production. The best thing to do is just sanitize your fermentation equipment and go from there. Sanitizing after fermentation with a nice heavy sulfite mix in a spray bottle (1/3 tsp/quart spray bottle) should ward off any bacteria floating around. Storage Sanitation - A good B-Brite solution to eat any proteins is wise before putting away fermenters. 1 tsp B-Brite / ½ gallon hot tap water. Coat all surface areas and let sit over night. Rinse well the next day. Spray with Sulfite solution and store for next use.
This is actually a complex question, depending on the form that you receive your juice, grapes or fruit. It is always good to know your pH and TA at the beginning, prior to starting fermentation. Juice can be tested immediately. With grapes and other fruit, a good test can be done about 2 days after receiving them. The pH and TA will change throughout fermentation. It is a good idea to test at least a couple of times during fermentation. Adjustment times are very subjective although you need a reasonable pH for starting wines. Too high or too low will result in no or slow fermentation. Significant adjustments are best done prior to fermentation, particularly big changes in acidity. Small adjustments or fine-tuning can wait until fermentation is completed. You can adjust your wines at nearly any time. Be sure to add the correct acid and remember that pH is for preserving wine, and TA is for flavor. Adjustments are often challenging and need to be done slowly so that changes can be measured.
Stems tend to impart some bitterness or woody flavors during fermentation. A small amount won’t hurt as it introduces a bit of tannin, but leaving all the stems in is usually not recommended. Experienced winemakers may use more stems in their wine and sometimes ferment whole clusters. It is a more advanced method and something not discussed here.
Winemakers will sometimes add Pectic Enzyme at this time to aid in the skins breaking down. Adding a 1/4 tsp Potassium meta-bi-sulfite (K-Meta) per 10 gallons of crushed grapes will help tame wild yeasts that naturally occur in the vineyard. Stir in evenly. It may make sense to add other additives if you are trying to correct specific issues with the grapes - acid too high or too low, inadequate yeast nutrients or other particular deficiencies.
Cold Maceration (Cold Soak) is not necessary, but may be helpful. The technique involves chilling the crushed grapes for several days (or longer) before fermentation. This can help extract some color or flavor compounds from the skins that are less soluble in alcohol. This is done right after you crush and destem. If temps are favorable (50 degrees and below) let fermenting bins with lids sit outside in the shade (or cold inside area), stirring grapes at least once a day. If temperatures are higher, you can cool the must with addition of dry ice, or ice bombs in plastic containers (so the melting ice does not dilute the must). Periods of 3-7 days are common. If there are any signs of mold or off odors, immediately bring inside, warm to fermentation temps and pitch the yeast.