A friend who's a florist is fantastic! You'll be in good hands there.
One of my concerns is your mention of an open bar all night long - that can get really, really expensive! Buy big bottles - the half-gallon (1.75 liter) size - for least cost per ounce. (See my Bigger Bottle, Better Buy article for details
http://www.bellaonline.com/articles/art69104.aspBuy 'well' liquors, too. That's the cheap stuff on the bottom shelf, not the premium brands you'd ask for in a bar by name because of their expensive advertising campaigns. I'll write an article later about different classes of liquor. Today's my Bella day anyway so you've given me a useful topic to write about
Will your open bar include a bartender? (Please, please say yes!) If guests pour their own, they make really strong drinks and they make them often. Your bar supplies will disappear quick. A bartender will keep the pour consistent and s/he'll know some tricks to stall guests who need to slow it down a bit - good for you and for them.
If you don't hire a pro bartender, ask a couple of friends to man that station. They can work together or trade off during the course of the evening so each gets a chance to mingle and party. Many people think of this as a privilege and are happy to do the honors.
My formula for estimating booze quantities is one drink per guest per hour. Some guests probably won't drink at all but others will drink more than the formula; they'll balance each other out. You know your guests, though, so adjust accordingly. If there are more teetotalers than drinkers, adjust quantities downward; if you're planning on a room full of party animals, adjust upward.
You'll be surprised at how much ice you'll need. If the party's indoors, plan on using 1.5 pounds of ice per person. If it's outdoors, have at least 2 pounds per person. Some ice will go into drinks both alcoholic and otherwise, some will chill beer and/or wine (depending on what you serve, of course). If you marry during a heat wave, have extra ice on hand. With our weather lately, 9-10-11 could be a blizzard or a scorcher but no worries. Ice will be one of the very last things you'll want to acquire and you'll know what the weather will be like by then. If you have an ice sales / delivery service in your area, call ahead and see if you can get a discount for quantity.
I don't know what New York liquor laws are like but here in Texas, liquor stores usually offer case discounts. That means a case of booze (6 of the biggest ones and 12 of the smaller liquor bottles and wine) is usually sold at a discount - 10% to 20% depending on the place. The booze can usually be mixed brands or kinds (2 rum, 1 bourbon, etc.), too, which helps a lot when hosting a big event like a wedding. There's a liquor store here I used to use because of the nice people, the discounts, and, if I bought the beer or wine at their store, they'd put the beer - the mead! - and white wine in their walk-in cooler the day before, so it'd be good and cold by the time I picked it up or it was delivered to the venue. Shop around for that if New York laws allow it. Any leftover booze keeps for consumption later, too, so excess won't go to waste.
There might be some cost-saving tricks to the drinks you offer, too. I still need to find you some suitable recipe ideas, along with that Guinness cake recipe!