To get rid of the co-pilot's MG go into the loadout screen (where you choose the fuel loadout) and at the top you'll see a list of weapons loaded. You can disable any kind of weapon on any aircraft just like loading/unloading palettes
As for your other observations, for the bomb impact spacing to work you need to have accurate altitude and ground speed values input to the bomb computer. If i set a bomb impact spacing of 30 meters, i'm flying at 2000m and 300km/h and the bomb computer thinks i'm flying at 1000m and 200km/h, i won't get a spacing of 30 meters but something else.
Furthermore, that data has to be your altitude and ground speed (not IAS, but TAS corrected for wind)
at the moment of bomb drop. In other words, if you want to achieve a specific pattern while dive bombing you have to estimate the amount of speed you'll be having at the end of your dive and use that value, along with the altitude you want to drop from.
The good thing is that IAS/TAS differences are smaller when you go low and since you are almost vertical and dropping from low altitude the wind will not have too much of an effect, so in theory you might just be able to get away with setting your release altitude and the terminal IAS of your dive into the bomb computer for diving attacks.
The inconvenience in all this is that you don't know what kind of speed you'll be having at the end of the dive beforehand, so you will have to do some practice runs offline and see what speeds you get at the end of the dive with your chosen power settings.