The motor is TWO horsepower. It should say on the info plate of the existing three phase motor. The big thing about voltage is the amount of current. A single phase 110 volt will require heavier wire because it will draw more amps. With the 230 volt single phase motor I used 12 gauge wire and a 20 amp dual pole breaker. If I recall it only draws a max of 8 amps at 230 volt. This would be 16 amps at 110-115 volts. All you need is three wires, two at 110 volt and ground. If you are not knowledgeable about electric wiring, this is best left to a professional. Electricity and wiring is serious business and not to be done in an unsafe manner, it can be extremely dangerous and life threatening, do not take any chances with this.
Follow the wiring from the electric motor. Where does it go ? Does it go to a six by eight inch electrical box on the vertical support ? There should be wires going from this box to the up/down switch. From the electrical box there may be a cord going to the three prong plug you mentioned. Basically the motor starter is a heavy duty switch that has thermal protection. The switch that you use to raise the lift just activates a solenoid in the motor starter to pull the heavy duty contacts together. YOUR SETUP COULD BE DIFFERENT. To let the lift down the motor is not used. The lever/switch just released hydraulic cylinder pressure.
The way the lift locks is to raise the vehicle to the height you want plus one or two inches and then let the lift down and the mechanical safety cams will engage against the H beam and hold the vehicle in place without the need for hydraulic pressure. Then when you want to let the vehicle down, you have to raise it a couple of inches to take the pressure off the cams, then hold the cam release lever (so they don't engage again) and let the hoist down.
I used an engine hoist to move the the slave post and the base around in my garage in the horizontal position. I would NOT try to use the engine hoist to lift the posts into position.
If you have 12 foot ceilings you should be able to rig up a temporary A frame type lift with a chain hoist or equivalent or some other type of equipment. Remember this stuff is fairly heavy and you must use safe lifting/hoisting practices.
There is nothing under the floor plate between the two posts. The cables go through the floor plate. The cables are protected by going through the floor plate. There is a channel for each cable approx 1.5 by 2.0 inches. Where the post sits on the base and is bolted there is a rectangular notch where the cable goes from the pulley and down into the base. To get the cables in or out you have to lift the post 4 - 6 inches for the ends to go through.
I have not used the hoist to store vehicles in a raised position because of this not being recommended for the type of vehicles I am working on. You get some frame flex and the suspension is fully unloaded. Some people say it is OK, what's the difference between four jack stands and a hoist ?
Regarding safety of the hoist, it is like every mechanical thing, use as per manufacturers recommendations, install properly, inspect and maintain components, operate properly. Remember there are four little pads that the car is sitting on. If one slips the car is only sitting on three and could fall. Newer hoists have locks for the arms to they cannot swivel. But if your pads are in good shape and the lifting points and solid there should not be a problem. If the lock mechanism is engaged, the hoist cannot come down unless there is some type of structural failure in a component. When locked the cables and hydraulic are not under any significant load. Remember need to let hoist down to engage the locking cams.
Personally, this type of hoist is best for working under the car without ramps in the way and the wheels free. For storage and some other mechanical operations the four post is the way to go. I also plan to install a four post when I can find a good used one. Mostly for storage purposes.