Thank you for the replies everyone!
You brought up some problems I haven't thought about yet thought about (recurved blades and serrated knives). The easier solution to getting a van's worth of gear is just to offer limited sharpening service for only the knives I can work on. Riding on a bicycle I think people would understand if I can't carry tens of kilos of equipment.
Sadden, thank you for your suggestions! I drool over the professional model, but it doesn't make sense in my case. I would be setting it up and taking it down quite often and on a bicycle, weight also matters (but it is way more impressive, I know... and probably has a few extra functions).
About the stones, I've read somewhere (I think) that diamond plates are not really suitable for sharpening metal... something to do with the diamonds becoming loose, I think... Aren't they meant mostly for ceramic knives?
This is not going to be my sole income. I have a job (a bad one, but that's another story) and this would be a hobby and some pocket money for beer and coffee for when I'll only be riding my bike in the old part of town, admiring all the long legs going by
In the best case scenario, I might have 1 normal client and 1 restaurant per day. If a client has 5 knives and a restaurant has 10 I can sharpen, and I charge 5 EUR per knife on average... (how do professionals usually set their prices? on the length of the blade?), that is 75 EUR in my pocket. And I like the sound of that. Even if I make half that, I'd still be happy with it!
Also, are the "stock" stones really that bad? Or can I use the lower grids and splash out more on the polishing stones and strops?