1.He didn't fail to stop the press,plus that was multiple powerups ago
2.He has defeated Ultrons before, in fact in Ultron unlimited he was beating 7 of them at the same time, it took an 8th Ultron(that was about 30 feet tall)showing up and then all of them beating on him and hitting him with 7 encephalo beams just to ko him
3.Correction, Kang tried, according to Wonderman himself, his ionic powers protected him from the blast
4. As for supporting part of the Island with the hydrobase(and a mountain), IIRC it's Avengers#307