I just recently bought slayer bot and im having a hard time setting it up. At the moment i haven't set up the bot to cleanly kill all slayer monster so it very slow in slayer xp and combat xp for me. But once i get it fully set, then im sure that i can run the bot over night.
But if i were you, i would get fighter first. Perfect Fighter is really easy to set up and can run all night if you have the right set of armor like full guthan and full bandos.
I make about 1m/Hr botting at abby demon. And that all i know how to make money with perfect fighter.