Yeah, it's correct if by "self employed" you mean "subsistence farmer". The US was basically a third world country in 1900. We only won the Spanish American War in 1898 because Spain was a dying empire.

50% according to this article. They mention 80% in 1860.

I'm not 100% sure of the source there but I have heard similar numbers around 50%. Think of all the self-employed people doing jobs that just don't exist today in the US - delivering milk, fruit, fish, newspapers, door-to-door salesmen, and that's on top of jobs that still exist today with a lot of self-employed people like AC repair, plumbing, etc...

From 1860 to 1900 the average size of American farms had declined from 199 acres to 147 acres and the percentage of farmers in the labor force declined from 58 to 38 percent.

No, doesn't seem right.