What watt power transformer should I be using?
You can use a power supply like the one pictured, rated for the amount of LED's you will be driving. Read the specs on the lighting. They should tell you how many watts per a given length of the strip. So if it says, for example, that needs about 1 watt per meter, then a 15-foot section would require a 5 watt power supply. Take your total length of 76 feet, and divide by the strip's requirements. It wouldn't surprise me if you ended up somewhere in the ballpark of 20 to 30 watts.
Can I run 14 gauge wire directly from a circuit 15 amp breaker to the transformer?
No. You can't put the power supply inside the wall, and you can't bring the wire out of the wall without going through a junction box. The best way to do this is to put a cord on that power supply, and plug it into an existing outlet. There is no need whatsoever to add a new circuit or connect these directly to a circuit breaker.
Can I plug in all 5 circuits of LED strips on top of each other to the output of the transformer?
Yes, you can wire multiple strings in parallel at the power supply. If the sections are short, you can also wire them end-to-end. Double-check the specs for maximum length of a single run.
Is this the recommended way of doing what I'm trying to accomplish?
The recommended way is to plug into an existing outlet. If your lighting requirements added up to 1000 watts, you'd want a new circuit. At 20, 30 or 50 watts, it is ridiculously small in household circuit requirements.
I would also like to add a on/off switch, do they make a wall switch for 12v?
Any switch can be used for 12v. I would put the switch before the power supply. Put a cord on the power supply like this cord with switch.
Can low volt wires come right out of the wall, or do they need a junction box before being connected to the LED strip lights?
The low voltage wires don't need a junction box, but they do need a junction plate, like those used for phone jacks.
Generally this is made of "Nope".
You hope to use flexible cordage.
Cordage needs to be correct for the task. A random extension cord won't cut it - believe me, I've struggled a lot to find longer cords I can put on 4' fluorescent fixtures. (I don't want to splice plugs on them, I want premade plugs).
Cordage needs to have proper grommeting/strain relief anytime it enters or exits a listed electrical box.
You can't attach cordage to walls. You might be able to run it through surface mount conduit.
You definitely can't route cordage through a doorway, whether there's a door or not.
Other than that, Mrs. Lincoln, use of cordage is not strictly prohibited. It's fine for the short jumper between a lamp properly physically mounted, and a nearby outlet which has been installed for that purpose. In fact, look "up" in a CostCo ceiling and you'll see a lot of that.
Maybe you should ask your landlord to install just that.
Speaking of that... The lamp needs to be properly hung from the ceiling. "any old way" won't do, it must be hung by a UL listed method. That is because if the lamp falls down, it will tear out its cordage, which will start a house fire or electrocute someone.
The home was provisioned to you with switched outlets along the floor. The purpose for those outlets is to plug in floor lamps. That is the right way to light the room.
If you like ceiling light... remember the terrible old halogen torchiere lights which stood 6' tall and had a 500W halogen bulb lighting the ceiling (which started fires)? Those were brought to market for this very problem. The good news is, today, you should be able to find modern LED versions that are maybe 30-50 watts.
Unless you investigate house fires for a living, you can't go with your own intuition of "safe". People who do... have written a big book. It's called the National Electrical Code.
The book is the reference standard used by insurance agents, prosecutors and judges. When a tenant violates Code, he creates a very ugly liability situation because the home insurer won't pay the landlord for the fire loss, leaving him to go after you. After you deal with the criminal justice system, you file bankruptcy to shake off the civil debt, and get a big surprise.
As a landlord I might be mellow about an alteration that was to code. But if not, I'd call the building inspector in, and he'd condemn the house and you'd be out. This method overrides rent control, 30 day notices and the like.
Best Answer
No. They're 12VDC, which means if you plug them into your wall they'll go PFFFZZZZZT and make a little puff of smoke. Or worse.
You'll need a power supply (a wall brick) that provides 12 volts and enough current. You can add mating plugs to the lights or just crimp them together.