I've used the fine dans stones without doing anything to them. Their lapping process makes them very settled in, and they're close enough to flat.
Other makers (norton, natural whetstone) have a coarser finish and need to be settled in and/or lapped.
As far as buying goes, were I to get more than just finishers, I'd get either:
* a vintage labeled washita that's known from the pike mine
* a hard stone that's originating from dans (black or trans doesn't matter). Naturalwhetstones black trans is a good dense stone, but it does need to be broken in
And if I couldn't find a good vintage labeled washita, I'd get what natural whetstone calls "hard" (it's only about $35 and is not a true hard like a trans or black). It can set a bevel in a hurry if you slurry it on one side and prep an edge for the trans on the other. I'd never go to the slurried side more than the first time setting a bevel on a razor that was way out of whack.