I started with a 1000/3000 double sided one, which is great for edges that are still sharp and need touching up.
I now also have a 200/800 which I can use to bring back edges that are well and truly blunt.
I also have an 8000 which I only really use for my razors, but I have put a kitchen knife over it too, just for shits and giggles. I shaved today with my Kamisori (see shaving thread) that I took up to 8000 grit. Best shave ever.
Worth mentioning that I also have a Belgian Blue finishing stone, which I am slightly cynical about.
Now that I'm getting quite good at this sharpening lark, and am doing knives for friends, my thoughts are turning to launching a business. I'll have a day a week free come September and am going to offer a local, sharpen in your own home service. I might try for some local hipster restaurant trade as well.
I'm gonna couple it with basic bike maintenance, punctures, chain clean and oil, brake tensioning kind of thing. Aimed squarely at the "family bikes in the shed with a puncture" market. Am in two minds about this bit as to do it properly I'll need insurance; which means qualifications; which means outlay; which means fiscal risk.
Best thought on name right now is "Steels and Wheels", although "Sharp as Fuck" is also highly tempting.
Would love to hear any thoughts.