If you're using a high proof liquor you typically don't need to pre-sanitize, but I typically do. You can either boil the jar for 5 minutes (timed) or rinse with bleach.

The more finely cut the fruit is, the more flavor will be absorbed.

I usually let them age for a minimum of 2 months, but up to 6 is preferred. Make sure to use ball jars with fresh wax seals and seal them while hot - once cooled, the lid should have a bit of flex to let you know the seal is unbroken. Make sure to mark contents and date on each one.

I'm most interested in doing herb tinctures (for cocktail additions) in dropper bottles. It's surprising to see that only 3 to 4 days are needed for said infusions. In your experience has this been the case? Keep in mind this would not be drank neat, but rather 3-4 drops used mostly for aroma.

I've only tried one infusion, ginger. It was grated directly into the vodka, left for ~2 weeks, and still turned out relatively flavorless. My ginger beer used about the same mount and was extremely sharp. Maybe I'll give it another go.