"spring underneath the drop safety" - I think you may have flipped the names of the safeties here so I'm just checking. The drop safety is the plastic ledge in the trigger housing the trigger bar rides on - #3 in the image below. I can't think of what spring would be sideways under it other than the trigger spring, so I think you meant to say the firing pin safety spring (#2)?
I have seen that happen before - typically it makes it near impossible to pull the trigger or keeps the firing pin from moving freely. Best to replace the entire firing pin safety w/spring (~$2).
However, that doesn't explain the double feeds, failure to feed and failure to eject. By double feed do you mean two live rounds coming off together or a live round shoving a spent back into the chamber?
Without waiting for your response - I'd start with inspecting the extractor focusing on the claw and replacing the spring loaded bearing and extractor depressor plunger spring (I would say inspecting the bearing and spring but who knows if they're worn down or not without a new one in hand to compare to)
Inspect the ramp on the bottom of the slide that strips the next round off the mag. I'd check the mag catch by taking the slide off and inserting the mag to test how they seat, if they move too much - there should be some but you want to see if the mag catch has issues.