Hi, I'm swamped with class prep right now, but I want to point you to my comment in a discussion of what the republics were like, which also includes a link to my discussion of the (failed) attempt at unification, which broke on the fear--humorously in hindsight--that the poverty-stricken and morally suspect Transvaalers would suck wealth out of the rich and responsible Free State! The major gold strike of 1886 changed an awful lot about their relationships, but only in adversity after 1896 did they really act in concert meaningfully.

There's certainly more to tell--the Republics were weird things--but this hopefully gives you a bit of a start. I can probably scoop more titles together, but I must know whether you can read Afrikaans because much empirical scholarship is only in that language and somewhat dated.