Parking can be tough. When I lived there, I rented a garage so I didn't have to deal with it. That being said, you can find parking, but it's likely going to be a meter, 1 hour or 2 hour parking. The thing is, they keep making the 2 hour parking take up more of the day. When I moved in it went till 6PM, now it goes to 9PM. Be sure to look at the signs.
Lower Haight has some crime, although it seems to be equivalent to crime levels in the Mission & the Castro. Parts of the Lower Haight are loud - with bar crowds on the weekends. Parking is difficult (though no more difficult than the other densely populated areas of SF)