I'm not certain if the original repetier firmware is fully Ardunio compatible, I think until fairly recently there was a modified version of Ardunio required for the repetier firmware... although I just loaded the Repetier.pde file in Arduino 1.0.5 and it successfully verified and compiled... Haven't tried uploading to my Rambo board as yet.
In Arduino
- Tools/Board (ensure you have the correct board selected, for mine it's the Arduino Mega 2560 or Mega ADK option... I have the Rambo 1.1b revision)
- Tools/Serial Port (ensure you have the correct serial port for your Rambo)
I don't believe there was anything else needed for Arduino... from my understanding the original Repetier firmware has LCD support, not certain if this needs to be enabled or not (it may be enabled by default)
When I say original repetier firmware, I'm talking about Repetier-Firmware on github as opposed to the SeeMECNC fork of Repetier which is called RepetierMAX (RepetierMAX is pre-configured for the RostockMAX) or any other number of Repetier firmwares running around out there.
There are two files which I believe are fairly important to ensure they are close to being right before uploading and that's Configuration.h and pins.h (especially pins.h)
pins.h defines all the pins on the Ardunio board and what is connected to that pin... (this is where I'm not sure, it's possible that these are a standard and you just select the right board.)
Configuration.h defines whether you want EEPROM, SD_CARD, what type of printer you have, how many steps per mm you motors do, how many degrees in the motor, how many teeth are on the pulley and what type of belts etc....
You may have received a diagram of the Rambo board with your Rambo, on this it will outlay all the pins. If you didn't get one you can look it up on the Rambo wiki, make sure it matches your revision. If you don't know, the board should have it marked somewhere...
There are various reasons why the LCD didn't display anything, the firmware didn't upload, the pins are wrong in the firmware, the LCD/board is wired wrong, the LCD isn't enabled. By what you've said sounds like the firmware hasn't uploaded... which is probably a good thing, make sure the settings are right first, I'm not sure if physical damage can occur if they aren't. The Rambo boards aren't exactly cheap at least not in my country.
If you do get to the point of being able to test the motors, have a finger on the power switch to flip it if things start going wrong. I presume you have End Stops, you'll want to be sure these are working and enabled before you can start trusting it.
Oh even though yours is custom, I presume you mean that you followed the wiki and purchased/sourced all the items yourself rather than buying a kit to build, there may already be a pre configured firmware for you (or a basis of one).
One more thing about the MOTOR_CURRENT, this could be either the variable needs to be defined or it is defined but the project wasn't opened correctly... How did you open the project? File/Open and selected Repetier.pde?
The pde extension came from the pre v1.0 of Arduino days, it should prompt you to 'save as' an ino when you save.
I don't currently know enough to give you definitive answers, I'm fairly new to the world of 3D Printers too, but I can give general ideas/pointers. There are others on this forum that maybe able to provide more definitive answers, but until they chime in I can help you to some degree.
Cheers