by mxk » Sat Feb 18, 2012 6:26 am
I've been using version 1.2 of the RAMPS for about a year in my main Sells Mendel and in a printer I've loaned to a friend, and have version 1.3 on my desk waiting for me to either finish printing the parts for a Wallace or for my Quantum to arrive, so I can claim a little familiarity with RAMPS, at least as a user.
Yes, most people set all four (or five if you have version 1.3 or later and want to experiment with dual extruders) steppers to 16x microstepping.
AUX3/SPI is what is used for the microSD card, lots of folks in the reprap forum have adopted them, and I plan to order a couple from Ultimachine in a few months. The SD card is not necessary if you are willing to leave your PC attached for the duration of the print job, but the general opinion seems that print jobs are smoother without pausing while getting more gcode from the PC.
I *think* you can use AUX1 for serial without interfering with any of the standard firmware, I suggest you contact Johnny Russell at Ultimachine to be sure; he designed the RAMPS.