doesnt that ruin the voltage differential through the line making there be zero voltage drop across the LEDs from the beginning to the next place where i hook up the 12 V+?
That is exactly what you want it to do. You want there to be no voltage difference between one +12V and the next. The voltage differance that drives the strip is between 12V and ground.
The normal way of powering these strips is to have a 2A power supply every so often on the 12V line.
Make no mistake so any LEDs is not a simple or trivial project. You are a beginner so you don't know what is easy and what is not.
You can get an SD card shield or solder one on. Again google it.
Even 900 LEDs is 18 amps, that is a lot of current and at 12V is over 200W, that is a lot of light to spread over a ceiling, get your sun glasses out.