I am current on the Cessna 340
it has up to 9 electric fuel pumps
2 in each tip tank, one to pump fuel from the back to the front of the rank and one to provide fuel pressure to the engine for priming and in the event of an engine driven fuel pump failure
1 in each wing to provide positive pressure and vapour suppression when the engines in feeding from the wing aux tank
1 in each wing to provide pressure to transfer fuel from the nacelle tank (if fitted) to the tip tank
1 in the nose to provide fuel pressure to the cabin heater
The fuel system is very complex and a full understanding of it is essential in order to safely operate this airplane. Depending on what pump has failed it can be a nuisance (eg no heat) to flight safety critical (engine failure)
As a general comment airplanes which have sat for a long time are often maintenance nightmares. I once ferried a Cessna 421 home for its new owner. The aircraft had a similar history to what you described. The snag list when I got it home had 59 items. For the first 6 mon5s it was in the shop after every flight. Eventually after a lot of hassle and expense the aircraft was brought to a reliable state but it was frustrating and painful. Even though the owner got a smoking deal on the airplane he vowed never again....