...I was drinking while I typed this.
Kayvan,
Just a few suggestions.
I wouldn't concentrate on having 4 of each types of liqueurs. Get yourself 1 good shooting brand (this will be the top shelf one) and 1 for mixing. For example: Vodka, do you like grain or potato? I prefer Potato - much better for shaking/straining over ice and shooting (Chopin is my favorite, good price point, smooth, no alcohol bit face which makes you look silly in front of friends). For mixing try the Russian Standard, It's a grain vodka and pretty darn good for the price and blends well. Absolute has too much of an after taste IMO.
Try the same with Whiskey - get a Bourbon to sip/shoot (Blanton's is my favorite). Get a mixer (Jack or Jim) for coke/sprite/sour. Get a blend for the girls in the crowd, Crown or Chivas - very different flavors. (but a Chivas, vanilla schnapps & coke is very good).
Gin - I prefer regular Bombay and 2nd with Bee feater. You can spend more but I don't see the point - you don't normally drink gin straight. The Tanqueray Rangpur Lime is a must - mix with sprite & splash of OJ for a summer all purpose tonic.
Single malt - I like the islays, they taste like gasoline from the peat smoking. You will have to find your flavor of scotch, they are all very different and you will most likely wind up preferring one type, tolerating another and hating the rest. To find your taste start by filling glass fill of ice, pour in a shot & add a couple ounces of water - this is destroying the scotch according to the scotch drinkers (& I agree) but it will enable to you taste the scotch and find the one you like - Then back out he water, then dial down the ice. Now you'll know and most importatn, enjoy your scotch. Laphroaig quarter cask & Bowmore Mariner are my 2 favorites. JW is a blended scotch - Red is too harsh, Black too sweet, Blue too expensive but ok. Dewars is also a blend and for the price the 12yr is pretty darn good, white is horrible. Scotch can be used to impress based upon the common accepted ratings - JW blue is rated as awesome but for the price you can buy 3-4 other really awesome single malts. I buy a case of JW blue every year and give it to my clients as gifts, they seem to appreciate it more than I do.
Rum - same, get a shooter & a mixer - aged rums are much easier to shoot (dark).
Tequila - Silver for mixing (Hornitos is excellent, reasonable & most important 100% agave). The sky is the limit with Anejo (aged) tequilas. Sauza Tres Generations is moderately priced and one of my favorites (and the one shoot by my relatives in Mexico). Herradura would be a 2nd.
Cognac - can't stand it, have nothing to offer here.
The IMPORTANT and most over looked - the cordials. Liqueurs like Tuaca, Baileys, Kahlua, Ouzo, Chambord, Gran Marnier, etc. These are what make mixed drinks good. Add a splash of Tuaca to a margarita and it will take the bite out of it for example. These are cheap and most popular with the ladies.
Keep some fresh lemons, limes & mandarin oranges - fresh mint, sugar & club soda.
For champaign you really only need 2 kinds (sweet & not so sweet). Veuve Clicquot yellow label for dry, demi-sec for sweet. Moet Nectar Imperial (black label) for sweet & White Star (white label) for dry. Korbel Natural (black label) is a nice "in the middle". Have a bottle of Dom, Dom Rose if you really want impress.
Just my novel & 2 cents. My house is better stocked than many, many high end bars. You will tend to gravitate to a few drinks you drink all the time. Most start off drinking some obscure, hard to make exotic drink. Then realize its a pain to make and and huge mess and get over it and settle on a Cuba Libra hybrid or something. Keep it simple - after all you will need simple as your accuracy will decrease as the night goes on. Don't try to measure anything - learn now how to mix by sight.
Yesterday it was Sailor Jerry's, Parrot Bay Key Lime & coke. Today it's Jim Beam Black & coke. Tomorrow maybe Mojitos... who knows. You will build up a tolerance, you Dr. & friends will call you an alcoholic (if they can't keep up) - you budget will increase and you will realize, after trial and error that you can find a really good $30/bottle that tastes just as good as the $60/bottle. But you may not be impressing as much with the $30 bottle. Buy the small fifths until you figure out your flavors.
Go too far and like me you will start telling the bar tender how to make your drink, correctly :biggrin
Enjoy!