Picnic taps are fine (i use three faucets and two picnic taps in my keezer) but just be warned that they DRIP. Once you've gotten used to pouring with them, you'll be fine, but when your buddy goes out for a beer and the puts down the picnic tap...drip, drip, drip all over your freezer floor which is so. far. down.
collar v. tower: i have a 9.5in collar. i like it a lot, but I also built the keezer up off the ground a few inches. I've always thought that it "feels weird" to pour a beer at waist level, so aesthetically I guess I like either a really tall collar or a tower. If I did it again....I might go with the tower, because it can really be a pain in the ass to lift that 5th keg over the lip of the collar and push it down into the crammed freezer amidst all the hoses and tanks and regulators and all that. Whatever you do, have fun with it and post some pics!