A few thoughts, I am not a jet pilot however mayby I can offer some thoughts. I have flown the 757-200 level d sim for 20 hours, with engine failures/fires etc.
I will obviously bow to superior knowledge of others!!
Take off probably Flap 15.
Regarding engine fire before V1... take off success will depend how far before V1 the fire/failure is. Just because you have an engine fire doesn't mean you have lost the thrust from that engine... however a loss of thrust from one engine significantly before V1 and electing to continue would be bad!
If the captain is flying during the take-off (I will assume therfore Captain is pilot flying), the FO would most probably call the failure e.g.. "Engine fire number 1" For your take-off they continue with a fire before V1. FO would make standard calls "V1 ....Rotate....positive climb". Captain callls 'gear up.' So the gear has hit a light. Well on one engine, overweight in hot conditions at flap 15 I would personally get the gear up to help actually climb! The lights are designed to break so hopefully not to do serious damage if an aircraft hits them.
Just to give you some idea the takeoff might proceed something like this...
At some point early in the climb captain would call to restate the emergency. FO would state 'Engine fire number 1' the captain would ask for the fire checklist engine number 1. The Fo would call and action the checklist from memory with the captain monitoring. e.g.
FO: Number 1 thrust lever close
Cpt: Confirm
FO shuts number 1 thrust lever (this could be the first moment thrust is lost from the engine on fire!)
FO: Number one fuel cock close
Cpt: Confirm
FO: Closes fuel cock
FO: Number one fire handle pull
Cpt: Confirm
FO pulls fire handle.
If fire still exists Fo would turn the fire handle to release one of fire extinguishers on the engine...starts the stopwatch. In 30 seconds if the fire still going, turn the handle the other way and hope for the best!