The short answer
You need very little for a tasting at home: a few small samples, matching glasses, still water, and a question you want answered. Everything else is just trimmings.
One question is enough for an evening
For example: How does the same whisky taste from two different casks? Or: smoky versus unsmoked? Or: malt versus blend? Start with similar strengths. If origin, strength, age, and cask all differ at once, you won't be able to say afterward what caused the difference. Two or three samples are plenty for a first evening.
More than three or four samples isn't a good idea. After that, your nose starts to tire, and the last glasses get an unfair judgment. Better to do two pairs on two evenings than six glasses in one.
Matching glasses, numbers instead of names
Set out identical, odor-free glasses, along with water and something neutral to eat, such as bread or unsalted nuts. Avoid perfume and strongly spiced food beforehand. Start with the lighter samples; smoke and heavy cask spice come later. This is a practical order, not a ranking.
Number the glasses instead of labeling them. Anyone who knows which bottle was more expensive will reliably taste it as better. That's not a character flaw — it's normal perception. Tasting blind costs nothing and makes the evening more honest.
Nose first, then taste, then note the finish
Write down three things in order: how it smells, how a small sip tastes, and what lingers afterward in the mouth. Everyday words are enough — apple, bread crust, pepper, campfire. Note whether you like it, too. Read the producer's description only afterward, or you'll simply find what it tells you to find.
And write it down before you talk. As soon as someone says "vanilla," everyone else finds it too. In a group, the first spoken impression is the most influential. So note it first, compare, then talk.
A few drops of water — in a second glass
If you want to add water, use a second small glass and just a few drops. That way you have a real comparison, not just an altered glass. Note whether the fruit, smoke, or the bite of the alcohol comes across differently. Also plan pauses with water, and set out something non-alcoholic alongside. No one has to finish their glass, and an evening like this isn't about being right.