Daiichi 5 and 6 can probably be brought back on line eventually, as can all 4 Daini. Daiichi 1-4 are clearly dead as reactors, but are going to be a b*tch to get buried. They should build a new fuel storage site for them as I don’t trust those damaged buildings for that purpose long term. Getting the fuel out of their ponds, much less the 3 fueled reactors will take a long time.
I think you are right about #4, but there isn’t a technical reason they couldn’t get it back up. It wasn’t running when the quake hit, so it’s reactor hasn’t had any issues. It’s fuel storage may have been breached, but that’s just a matter of requilding the exterior building.
However, that reactor is old, and was shut down I believe because they were looking at whether it could be upgraded. So it is quite possible that whatever economics made that feasable, the added costs of rebuilding everything damaged by the explosion would probably push it into the non-economic territory.