a. Generally speaking, you're only able to transcribe spells from a wizard's spellbook, but the wording on Blood Transcription is a bit iffy. It says "using the normal rules for copying a spell from another source." The normal rules are that the source has to be a wizard's spellbook specifically. However, I could see this being interpreted simply as you must follow the general copying rules... so you might want to talk to a GM about that, because I'm no help at all here
c. I believe so, incurring standard penalties.
d. There is no RAW ruling on that, but it is a bit ridiculous to think that an alchemist could drink something from a hidden hand without his head being concealed as well. It's probably intended that a bonus arm can't remain hidden and perform obvious actions like attacking or drinking a potion.