Welcome aboard. I started in OB and I remember it being tough in the beginning. Just hang in there.
The number of doors you are assigned are dependent on how big the plan for OB is. I've seen days where I was staffed with only 3 doors, and days where I've had to run 10 doors. I would ask your OM, LWW or closer for a staffing sheet so you can see how busy your lanes set is going to be.
You should be working your lanes set alone, but if you can reach out to your closer or LWW and see if they can give you a hand for a few in order to help out.
The yellow light means that your lane is full and that no more cartons can drop down or divert to your door. That light should be your priority. Depending on your building you should have a yellow and white light. The white light means your are 75% full. If you have no yellow lights on they're your next highest priority. If you have no lights on your priority should be your busiest lane.
And yes, rough handoffs, are unfortunately normal. If it's really bad, inform your OM at the start of shift, so they can take pictures and provide feedback to the other shift.