the high yields for step 1 are path, pharm, micro, and physio. you should certainly study your embryo, but don't invest too much time there; put it in the aforementioned 4 subjects. on step 1, you might get some questions on a structure deriving from which aortic arch/pharyngeal arch/brachial arch, etc, and you should memorize those b/c they're easy points, even if there might only be 3-5 embryo questions on the whole exam. but definitely know the anatomy in FA.
as you go through uworld, you'll see how almost anything or any word in FA can be tested [hence you'll be advised to know it inside out]. certainly read and try to memorize all the embryo in first aid (i.e., you've been exposed to it once) b/c it can pop up on step 1, but don't invest the same time in that as you would for cardiac pathology (i.e., you might get more murmur audio questions on your step 1 than embryo questions total]. absolutely do not consult outside resources for embryo; just know what's in FA and UW. good luck!