"Restricted" GPIO's and max. current output of +3.3 and +5?

[freedomlives]

I'm making a home controller / alarm system from the A20-micro board.

Right now I'm designing a breakout PCB to connect to one of the GPIO ports. Wondering which GPIO pins are "restricted" -- e.g. would break the function of some on-board connector? Like I see on GPIO-1 some SDC1 pins, which I assume are connected to the larger SDcard holder. I'm thinking that GPIO-3 is the "best" of the GPIO connectors to use, as that is where most of the EINT pins are, which could be eventually interesting to use instead of constantly scanning in software each pin, though I wonder what all ATA pins are for there-- are these for the SATA connector?

Other thing I can't find is a specification of what is the max power out of +3.3V and +5V pins? For the simple door/window contacts, I was thinking just to directly supply their power from the +3.3V pin, and then run through a resistor back into the GPIO. Likewise, I have some small 5V relays to drive, 300mW coil power, as well as some temperature sensors on a slow and long I2C bus. It would, of course, be possible just to add an extra DC-DC converter for this from the +12V power supply that will be powering the board and active sensors like motion detectors.

[LubOlimex]

I can't see SDC pins on GPIO-1. Both SD card connectors are NOT routed to the GPIO headers.

Inspect the three GPIO headers in the schematic - you can use pins that in the schematic have just the port name (e.g. "PH7", "PG2", "PE2", etc). If they have some other longer name like "PC3/NC1" or "UART0-RX" or "ESC_BUT" these are used for something else too.

It is safe to draw up to 2A at 5V and up to 1A at 3.3V at the same time, as long as you power supply can handle it.