class 1 road test right turn only when green light

1) Unless otherwise marked with signage In Canada you don't have to wait for a green light to turn right unless the right turn is a dedicated right turn light all by itself. The USA may be different because they are a patchwork of sovereign states in a republic union.
2) Yes that's correct. You must only turn right when the blinking/solid right turn arrow is lit green. If there is no dedicated light, there will usually be signs indicating that you cannot proceed until green. You must obey the sign regardless of what other lanes of traffic are doing because that's unrelated to your own right of way.
3) Semi Trucks can use as much roadway as they want, without penalty. You're still responsible for any accidents that happen when you proceed to an incursion onto other lane so that's your caveat. You're also responsible if someone sneaks beside your trailer when you're turning. If you're backing in off of the street you're still responsible for any accidents that happen. While you may be allowed to turn right on a dedicated light and merge at the same time as dedicated left-turn vehicles opposite you merging into the same lane as you, you'll be in conflict due to the size of your vehicle. You can legally use the rightmost lane to merge to the new street, and left-turn vehicles can legally use the left most lane when entering the new street. You can still make the turn but you'll have to move over two or three lanes from where you came ahead of time (buttonhook turn to prevent people from cutting in) from so you can make the right-most lane and not incursion with other traffic in the left lane

That's one of the major stress points of being a semi-truck driver. You should always mitigate this risk by being disciplined in your smith system scans. This skill will be incredibly important when you're finally dispatched to dense urban environments like Chicago or Los Angeles, or New York.

 

There is no harm in always waiting for the green light. In fact if you don't have good line of sight of oncoming traffic it would be of due care and attention to do so.

Before taking the driving test you should always get enough hours of practice with an instructor so you're more aware of the time, distance, and space you need for the turning circle of your trailer and the lead space you need for your tractor to lead your trailer. Also, intersection sizes are all different even if they don't look like it, so knowing how much space you need independent of the road in front of you is a valuable skill long after the road test. Truck routes are always designed so you can make the turn without cutting across too many lanes. 16 Lane intersections (4 lanes each way) come in all shapes and sizes.

Always practice with the trailer tandems set to 41 Foot unless you are going into an old section of downtown with narrow streets. Don't let your instructor cheat you and set them all the way forward to 38 foot because that won't get you a real sense of the space involved.

Also when in doubt, cut across the lanes ahead of time as much as you want before your turn. It's better for your trailer tires because they won't scrub as much rubber off as you would in a tighter turn.

Don't rush training, and don't worry about the $5000 you're going to spend on road time with a quality instructor. Female instructors are the most brutal and savage so try and find one of those to teach you the ropes first.

To communicate with your instructor better get a model toy truck-trailer set and have your instructor show you with the model how the maneuvering should look and work. Then take that and practice in real life. Your drive time should always be about demonstrating the mental model your instructor is trying to teach you.

For left turns on truck routes in very large intersections there is usually no need to take more than the left turn bay lane, but for smaller intersections or intersections with tighter than 90* angles you may have to cut into the lanes on your right before the intersection, or there may be no space at all to clear your trailer so you'll always be in the right lane to begin with long before the turning lane starts. There is sometimes signage indicating that trucks are only to use a dedicated lane for turning left.

 

Practice your buttonhook for right turns.