You need to think about what kind of things will end up in the flare drum. A typical problem is LPG's that have a low temperature boiling point. Any pump you put in will have flashing problems. When the cold liquid hits the warm pump, instant vapor lock.
Next, using a staged pump system is a good idea. The first pump comes on when a level is detected and a second comes on when the level is even higher. Again, thinking about what can be in the drum will make a difference on the pump design because of different densities.