All Hallows’ Eve isn’t for a few more days, but the Halloween celebration starts in earnest now. But it’s not all ghouls and goblins and slutty pumpkins in Milwaukee this weekend. An eclectic ensemble takes the stage at Uihlein Hall in the Marcus Center for the Performing Arts, 929 N. Water St., for “The Arts Bridge Project: A Century of Song.” Performers include soprano Alyson Cambridge, cabaret star Scott Coulter, Milwaukee’s Florentine Opera Company, the Milwaukee Ballet, Sista Strings, TRUE Skool, the Jamie Breiwick Quartet and more. The show starts at 7:30 p.m. Friday; tickets start at $24. Info: marcuscenter.org Scores of area bars are holding Halloween costume contests this weekend, but on Brady St. Saturday, they’re doing it bracket-style. For Halloween on Brady Street, 14 participating bars are holding costume contests, with the winners competing for a grand prize at midnight at Regano’s Roman Coin, 1004 E. Brady St. “Huge” cash and beer prizes await the winners. Info: bradystreet.org Two very different approaches — but both very colorful — to the season come to the Mitchell Park Domes, 524 S. Layton Blvd., Friday from 6 to 9 p.m. The Tropical Dome hosts “Ghost Under Glass,” a not-too-scary haunt with activities, candy, games and prizes, while the Desert…