One more thought (sorry to keep dumping ideas on you
), if you run a pump externally, use flex PVC or at least vinyl hose for the connections to the pump. If you go rigid PVC all the way, the pump vibrations transfer into the plumbing (and sump) and you get a hummmmmmmm kind of effect. Also a mouse pad works well for under the pump to further dampen any pump vibration.
Flex PVC is the best, works/glues exactly the same as rigid PVC, same fittings, etc. you can pick it up from Western Pump in town. You can also get unions there (although some Rona's do carry unions now - nice
).