This objection needs to be corrected:
"You need the gear ratio, this should never be an integer, so a single front rotation should never result in an integer amount of rotations of the rear wheel. (not really a question, an objection)"
The reason of my objection was wear. But as long as the number of links in the chain is no multiple of 2 or 5, it should be ok.
When 2 gears (including chains) interact, having no common divisions is a requirement. Say you have a 50 tooth gear and a 100 link chain, each tooth will interact with exactly 2 links only, which means that any damage to either a tooth or a link will be interacted with only a single tooth or link which will damage that one. The effect will be other way around as well causing massive focused damage, which will cause the gears/chains to break.
Similarly, when you have a 50 tooth gear and a 25 tooth gear after a chain, damage to a single tooth will cause a small shift in torque on each rotation. This small shift in torque will always be applied at the same teeth in the second gear. The effect is smaller when compared to a direct relationship. This is applied in machine construction, but I have learned it isn't applied for applications such as a bike, the effect is negligible or the cost to replace gears is relatively small.