Well, the solenoids (shown lying on the ground outside the valve box) should be threaded into the fairly obvious locations on the valves. The knobs in the center of the valves are called flow controls and will regulate the amount of water that passes through valve when it is open; more than likely these could be left where they are. The screws indicated in your picture are manual bleed screws these can be used to manually actuate your valve (turn it on/off). As for why there are both a ball valve and a gate valve, who knows perhaps whimsy on the part of the installer or some situation where an additional valve was necessary; maybe the gate valve leaks? I would recommend you thread the solenoids into the valves and fire the system up, it should work. The only issue I see is that the valves may not correspond correctly with the indicated position within the clock; some trial and error may be necessary to get the solenoids back where they belong.

You can attach a fitting to the test cock. Set your compressor to 40 psi Max. I have a drain/waste valve in the house that supplys the water. I shut the water off and remove the waste cap. I screw a compressor fitting over the hole and purge from there. Done it for years. No problems. Again, keep the pressure down.

you've done a good job. the only other thing you can do if you expect an extremely cold winter is connect an air compresser to the outside hosebib and manualy open the valves to clear all the water from the system.

See your other thread http://forums2.gardenweb.com/discussions/4213792/pvb-backflow-open-or-closed-during-blowout?n=1