I think the best thing to do first is to get the amp to turn on and working by itself. That, in and of itself, is fairly simple. I can't tell in your pic, but if the power transformer has two black wires coming out of it, those are your 120 VAC input and all you need to do is to study it and see how you can simply add a power cord to the two black wires. After you figure that out, then you can just add a switch in between the hot wire and the wall socket.
Then I would deal with the input. It is a single input from the tuner to the amp (I also own this same tuner and amp) and is a line level input. The original turntable's phono cartridge was ceramic so it is basically line level.
Since the turntable plugged into the tuner, selecting phono would have been like selecting another line level device like a cd or tape deck.
The tuner has its own built in power supply so it can run independent of the amplifier so if you wanted to keep it around, it makes for a spare tuner which works pretty well with other integrated amplifiers.
Without a schematic, you would have to look at its power transformer just like the amplifier and see if it also has two black wires coming from it. Mine is wired with a power cord and female RCA's so I can use any set of patch cords with any integrated amplifier.
If you would like, I would be more than happy to take pics of mine and show you how to wire it up......if you want to keep and use the tuner separate.
My amp is pretty much in a permanent location at the moment but that wouldn't help anyway as its had all of its phenolic sockets removed and is wired with RCA jacks and permanently on when plugged into the wall. It plugs into the power receptacle on the back of a Kenwood preamp so when the preamp is turned on, it also turns the amp on.