I don't know how much is too much, but if it seems like a lot, you should probably call your Dr. ASAP. Could be acid reflux and the acid may be affecting his vocal chords, hence the hoarse voice. IDK, its worth asking you Dr. :-)
Having a hoarse voice in addition to spitting up a lot is a key sign of acid reflux, which can be caused by food allergies (especially dairy and/or soy). If you are breastfeeding, try eliminating dairy from your diet and see if that helps. It could also be that her valve that keeps food down is too weak and causes her to spit up. I'd talk to her dr about it.