Can you answer the specific questions ?
Q1/How should I know that I could use those pins, given the schema in my first post and the pin planner in the ossc project. I find it very hard to determine that those pins are indeed free.
Pin 28 for example says SD_DAT2 — What does this mean? Why is it there? If they are not used in SPI mode, then why are they labelled as in use on the schema? Are you now saying Should I just ignore that? How am I supposed to know what is what?