By SARA VANDEN BERGE   The inaugural Dowell Ace Hardware Home Improvement Vendor Expo is coming up and this is one event you don’t want to miss.   The expo will be held from 4-7 p.m. Thursday, March 12, at City Hall at City Limits in Stephenville.     The event is designed to bring together homeowners, local businesses and industry professionals for an evening showcase focused on inspiration, education and community connection.   The expo will serve as a central hub for home