The migration message is just a side effect of moving the gun prototype later into the data stage - you don't need to worry about it, it's not an item you'll ever be able to obtain outside of the editor. The recycling recipe is something automatically generated by Quality for every item in the game, the only difference is now the gun prototype is added after Quality generates those recipes, so it isn't able to generate one for the gun prototype. It doesn't matter anyway since the prototype isn't craftable, it's just there to tell the turret and wagon how to behave. (The name is just because I followed the vanilla Factorio naming convention and it calls the artillery gun prototype "artillery-wagon-cannon" for some reason, it's not talking about the actual artillery wagon.)
The distances are more interesting.
-
The automatic distance is exactly what I'd expect: it's the automatic range of the vanilla artillery, multiplied by the 0.8 multiplier basic artillery uses. If that's too short for your needs you can change it in the mod settings, anywhere between 0.5 and 1 (i.e. half of vanilla range and full vanilla range).
-
The manual distance is way, way higher than it should be, and I'm not sure why. I suppose I'll have to look into exactly how that mod you're using works, though it should be said that it's intended to apply to vanilla artillery only (pretty explicitly in the name, actually) so it might not be making changes in a way that I'm able to interact with properly in my mod without making a specific edge case specifically for this mod. If it comes down to it I'll probably end up doing that but I'd prefer to have it work more generically if possible.