Literally, the more stuff/structure you put in there, the more places bait fish and all the other fish have to hide and spawn and that makes for more and bigger fish. Anything and everything is game. Doesn't look like you have a lot of trees directly over the pond to dump in leaves so you'll only have to worry about muck sediment washing in from runoff. If you haven't already, put aeration in the pond. I'd put in 3 bottom bubblers running off a single air pump. Air pumps run very cheaply and can move a lot of water from the bottom to the surface riding the bubbles up. If you do that now, you'll keep muck from building up in the pond from the start up. It should stay that way for many years. You'll keep the pond and the fish happier too. I own a pond dredging company so I see a lot of ponds and a lot of pond problems.