Personally, I would want to keep the fruit on the tree...
I do think that it looks like it's been getting entirely too much water... and... bringing it indoors will always result some in leaf drop at my house.
I'm not sure that you'll be able to repot w/o losing lemons... How long has it been in that same pot?
At my house, I had one in the same pot for an ungodly length of time... 5 or 6 years, maybe longer... it was really suffering... set it out in the garden this last growing season... big improvement...
Personally, I'd stop watering for a month or two... see if that helped before doing too much else.
Edit:
just re-read your second post...
I wait until the end of winter before pruning... but autumn is my preferred time for repotting... I never do them together.
