With some luck, $18 million and buy-in from new industries, the now-defunct Ansonia Copper and Brass site could spark a renaissance for the entire Valley. That’s the optimistic view that local officials have in their sights, helped out by a new 200-page plan that predicts the 116-acre complex could become a manufacturing center again with thousands of jobs and the need for the amenities those workers would desire. If the site can be developed as presented, the plan estimates that at least 1,800 full and part-time permanent positions involving both light and heavy industry, office and clerical jobs would be created. Another 225 full and part-time construction-related jobs would be needed during construction. Officials predict it will take $8 million to $10 million to demolish at least six of the seven remaining Copper and Brass buildings. One, the 175,000 square foot extrusion center built in 1895 and last renovated in 1944, could be preserved.