- Going by Ironheart’s figures, there should still be hundreds of thousands of sane telekinetics… Would have been nice to have a line saying that, I don’t know, the more powerful a telekinetic, the less sane they are and that the ones that can function in society have almost negligible abilities…

That bothered me too, and I like your explanation. Or it's an unstable ability, that comes and goes, or you lose it or it weakens as you grow older.

So, why didn’t the Psi-Corps continue with the experiments?

I always figured that they did, but didn't get them replicated successfully before they were shut down after the war. It also might have been a combination of something in Ironheart himself and the treatments, rather than just the treatments. I disliked the 'kill the researcher so no one can do it again'. Didn't the man keep notes?

Fresh food is rare and expensive, and generally has to be imported from Earth. But then we get the view from the monorail, and there’s apparently miles of green parkland around a huge open area

They would need the plants to assist in air recycling though. And while animal products are rare (bacon and eggs) except for G'Kar's sources of hogsheads, there seem to be fruit and vegetables (oranges for sale in the Zocalo on pushcarts, Susan's salad). Doesn't jive with the breakfast slop they have to eat, but maybe that's to toughen up the officers :)
They might lease parts to other governments to grow their own required grains, etc. Or require acres for the nutritionally balanced grain (quadritriticale?) that goes into making breakfast slop.