Hello,
I also wouldn't use chains - even though it is possible of course.
First: using a chain without gearing means coarse step resolution and very little force. If you compare for example a screw with 5mm pitch and a sprocket with 50mm effective diameter you get 0.0125mm step size for the screw and 0.39mm step size for the chain (with a standard 1.8° motor). Also force is about 20 - 30 times lower for the chain. Microstepping will help a bit to improve resolution - but microstepping angles are "soft" - the more torque needed the higher the deviations and it won't help to improve force. You'll need a very strong motor or need a gearbox.
With this in mind you can select a gearing ratio depending on sprocket diameter. At first it would be reasonable to keep it to something that is more or less comparable to a spindle. In this case with a 50mm wheel it would be something around 30:1 - quite hard to make - you'll likely need 2 gear stages. So if you have a strong motor you may use a lower ratio - this will also increase speed but precision will be worse. Next consideration: your gear should be more or less backlash free or you'll have a lot of backlash to compensate especially with 2 stage gear drives. Timing belts may be a good and reasonable priced choice.
There is one last especially bad thing about sprockets with low tooth number: "polygon effect" -> the travel your chain will make with each step is different depending on actual sprocket angle. With a 10 teeth wheel it is about +-2% - with 30 teeth only about +-0.25% - so a large diameter wheel is more precise but also needs higher gearing ratios than a smaller one.
My personal conclusion: unless you have very good reasons to use a chain (extremely long travel of several meters / a lot of dirt / very high forces) - don't use them. You won't save money and precision won't be too good.
Christian
My CAM Software and CNC Controller: www.estlcam.com