Manual Steering ratio, recommendations? 16 or 24 to 1?

20 to 1 is a good compromise

X2 on this. 24:1 means a lot of turning-turning-turning to get around a corner. 16:1 handles super when in motion but sucks at low speed - aka parking. 20:1 should be just right. You might want to think about a slightly larger steering wheel, it really helps when manhandling the thing into parallel parking spaces.