It isn't unusual for the bottom leaves to fall off on tomatoes, especially indeterminate ones, at least not in my experience. When the soil splashes up onto the leaves it usually causes bacterial speck/spot/etc, which may be what you are seeing. It's always good to mulch tomatoes. Mulch helps to keep the soil consistantly moist (helps ward off BER) and also prevents (to a degree) soil-born problems.
I have noticed that if my tomatoes become stressed that the flowers
do shrivel and fall off, much like you've described. Right now, I think part of it is the heat and humidity that suddenly exploded here in KS. I'm not sure what other factors may play in the flowers
dying off. This is stretching past my knowledge here, but maybe it could be that the plant is already producing all of tomatoes that it can and must let the blooms die or possibly a deficiency in the soil of potash/potassium. I'm sure there are other causes too and I am not aware of them.