Point #5. Yeah you can, but its not feasible. You rather just turn the unit around and lift up other objects. Reasons:
The opposite end of the one side with the forks on it, should have a counter weight. So, for 2 sets of forks on either side, you would need to have 2 counter weights, doubling the load on the puny machine right on the get go. also the full length of the fork lift will increase, possibly making navigation through narrow turns etc difficult.
If you have both sides with forks, turning may be an issue, as one set of wheels will be used for steering typically the back, and since there will be a load on it, it will make those motors huff and puff when turning, most likey leading to undesired operation, you turn to full turning capacity, but it only turns to 75% due to the load on the wheels.
Having only one set of forks is great for this, due to when loading the forks with a crate, it reduces the weight on the back wheels a little, the steering wheels, making it a little easier to steer.
This covers point #2 aswell.
Google "arduino servo control", there are many links. Even some videos.
Even for remote control, google it.
You are gonna need a voltage regulated power source for the Uno. Get a 9V supply, and step down to 5V with a regulator.
How far along are you at the moment?