The electric mining drill is quoted on the wiki as having a "Power" of 3, and a "Speed" of 0.5. But I don't see how I'd translate that into a rate of production (something like N units of copper/iron ore per second). Similarly, a normal belt is quoted as moving 1.875 tiles per second, but how many items can reside on a single tile? And a stone furnace is quoted as a "speed" of 1, but one what? Unit of ore per second? Also, inserter speeds are 1 or 2.4. Again, is that units per second?
I've seen rules of thumb, like a normal belt can accommodate up to 8 drills per side, or an electric furnace can process exactly one drill's worth of output. But I don't know where those values come from.
I understand that lack of power can slow things down, as can modules and technology such as inserter stack size. For now, I'm happy to ignore those factors - I'd just like to know how to do the basic calculations for a starting factory.
Can anyone help clarify? Also, if there are better places to get the data I need than from the wiki values I quoted above, I'd appreciate knowing that - but preferably not from in-game, as I tend to do my planning "off-line" - when I have access to actually play the game, I usually do that, rather than planning

In case it's not obvious, if there's something I missed on the wiki or similar that explains all of this, then a pointer to the information would be fine

Paul