[oil pan 4]

Well if you want to move cars then you get a car hauling trailer.
Problem with cars is they are kind of heavy and they are a moving point that starts at the back of the trailer then rolls forward on to it.

You are likely not going to put a car trailer in the garage on its side like one of those throw away northern tool trailers. A decent cheap and small car hauler trailer weighs around 1,500 to 1,600 pounds.
I am not saying it cant be done just that you are going to spend more on this tilting system then you are on the trailer its self.
I don't think you are going to be able to bolt extensions on to make it longer. Again a car hauler is not a trailer that comes in a box that can be bolted together. Besides it sounding like a really bad idea over all, when you register the trailer they are going to require a length and width, if you change the length then that's not the trailer you registered. Now you have invalid registration and the trailer is confiscated.
Anything with a deck over 6 feet wide is going to have to be a deck over axle trailer so the deck is going to be high off the ground.

I already built a do all deck over tandem axle trailer. It weighs about 2,000lb empty, the deck space is just under the legal limit at just over 8 feet wide on the deck, 101'' wide over all and just over 18 feet long. The deck and supporting structure is made to handle crazy point loads and it will carry loads of volume. It has two 3,600 pound axles on it now because that's what I had on hand when I built it. I built the trailer to eventually have 5,400 pound brake axles.