Determining suitable wire gauge for LED-strips (voltage drop)
Correct?


Yes, the cable will cause a voltage drop of 0.54V at full current. However, in your case it is probably not critical that the LED's have exactly 12V. 11.5V is probably acceptable. 5050 LED's (a size of LED) have many manufacturers so check the datasheet (if its even available, many Chinese supplies make them hard to find or don't release datasheets). I think that most 12V LED strips would run fine with ±0.5V, most of them are using a PWM scheme to drive the LED's. 

Many power supplies have means to adjust the output voltage (usually by a trimpot on the supply) so if the supply has this feature, you could adjust the supply to 12.5V to compensate for the drop in the cable. 


  Does this mean that the LEDs get 11.46V of voltage or 11.72V (minus half of 0.54V, because they are halfway on the circuit)?


You can think of each portion of the cable as a resistor, so the second voltage drop for the second part of the cable will only need to be calculated with the current that is running through it. 


  I am assuming that a voltage drop of at most 0.54V is acceptable for these type of LEDs. Is that correct?


Probably, again one would need to check with the manufacturer to find out. Or buy one strip and then connect it to a bench supply and set the voltage to 11.5V to test.