There are propulsion and radiation issues for manned GEO missions. Most sensible ideas for large GEO platforms constructed in orbit involve assembly and checkout in LEO, then transition to GEO of the final assembly without humans. A short manned maintenance mission after the platform is on GEO station is more practical than an assembly mission, since it would involve less propellant than hauling the whole platform back down to GEO, and a maintenance mission would be a lot shorter.

Or even safer, use remote operational handlers for GEO maintenance. An unmanned small spacecraft would deliver spare parts, and remote-operated robotic arms (similar to the one already on the ISS or even better) would take care of the changeout. It might not be a bad idea to equip the original platform with a nice cache of spare parts in the first place.

Such platforms could be space telescopes, power satellites, or large array comsats capable of working with very small transmitters on the ground.