I think either cut a hole in the glass/acrylic lid to fit the piece of wood or build a box on top of the tank and have more wood sticking up with plants etc as per that other one I showed you.
As for the plumbing, you're going to need some MASSIVE flow for a tank that size with the stock you're planning, I would look at running three drains in your overflow, drilled thru the bottom if possible. The first has a tap on it to adjust the flow and runs as a full siphon taking as much of the flow as possible (there was a post on MFK showing flow rates for pipes, and a 50mm pipe at full siphon will flow a HUGE volume of water). Obviously a full siphon not sucking in air will be silent. The second drain has a durso on it and handles the small excess of water not taken by the first, and because of the small flow and the durso it should be nearly silent. And the third drain is a back up so that if something blocks one of the first two it won't flood your lounge. Search for "bean animal overflow", its more commonly used on reef set ups but could easily be used on a massive FW tank if its in your lounge and needs to be silent.