depends on what harmonics you have added, personally I would high pass it, and put a pure sine in there, and keep the harmonics above the sub - some people like the extra harmonics, just be careful not to muddy up your kick, and be careful with your compression, and u'll be fine either way
Depends entirely on what your distortion did. It may have increased the volume at 50hz.
Use your ears or a spectrum analysis to check how the perceived and actual level of your sub changed. Also if your distortion added the 2nd harmonic (100hz), you will most likely want to notch that out with your eq as it will almost certainly conflict with your kick and also reduce the perceived level of 50hz. (Kind of like what miszt said.)