Vodka acts as an extract solution. Soluable in alcohol more than water.
Not unless you add a LOT, the flavor will not be impact by the vodka. This is the only way I add spices to beer. I use 8oz of vodka to steep my orange zests and coriander, for example, on my Wit beers and there is no vodka or burning alcohol taste to the beer.
You want to use a measured amount after pulling samples and dousing each with specific amounts, you can then do some simple math to tell you how much you need for the entire batch batch. BTW add it to bottling bucket, not primary.
BTW Cheap rot gut vodka works great.
Kegged: Millenium Galaxy IPA, German Pilsner. Apricot Blonde Ale, ACE Witbier, ACE American Wheat.
Bottled: Smoked Red Rye, Old Tanglefoot Barleywine, Tripel, Dubbel, American Farmhouse Ale