This is a fairly obvious question, but how did Kramer earn his living? Obviously he borrowed groceries from Jerry, but that didn't pay his rent. Was he on the government dole? Living off an inheritance? Apartments in NYC aren't cheap.

My guess is he survived off his winnings at the track. His father was a "Mudder " his Muther was a"Mudder"!

Didn't he live on some sort of settlement from H&H bagels? Burned by coffee or some such?

Paul Buchman from Mad About You was actually paying rent on Kramer's apartment and had forgotten about it.

Didn't he live on some sort of settlement from H&H bagels? Burned by coffee or some such?
The settlement he got for being burned by coffee was free coffee for life. No money was involved.

The H&H Bagel thing is a little more complicated, but IIRC he was on strike for 10 years. I suppose the union could have been paying him some sort of money from a strike fund, although I doubt there was even a union involved, and I don't think they would keep that up for 10 years. In the episode where he went back to work, they fired him.