38/f h/o subarachnoid hemorrhage 6 m back, suffer daily headaches. Safe to get pregnant? Nullipara.

Probably not. I would recommend you meet with a high-risk maternal fetal medicine specialist to discuss the risks of getting pregnant at all, let alone within 6 months after this incident. It isn't impossible or necessarily unsafe to get pregnant, but the goal is to discuss the challenges that will be involved with a pregnancy. I agree that it is very important to try and find the cause of the hemorrhage.
Depends. Depends on what caused it, how big was it, and how was it treated. Daily headaches sound like not fully healed, and pregnancy is a high volume state, so I would wait til headaches resolved then reassess stability.