I'm about to place a water storing tank at ground level and connect the water feeder pipe at the bottom of the tank. Would water fill normally as the top filling? Would atmospheric pressure + water mass pressure cause water feed pipe to stop following water?
If the pressure in the supply water line can force water up the outside of the tank and over the top, above the tank water level, then that same pressure can do what you want: force the water directly into the bottom of the tank against the same pressure head.
The problem is that, by making the direct connection at the bottom of the tank, you have no way of preventing a backflow of water from the tank, if the supply pressure drops below the pressure in the tank. If this backflow is into a city water supply, then this is a major safety hazard, and forbidden by most codes...
Yes you can. Feeding the tank from above will exert the constant maximum head on the pump until the tank is full. Feeding from bottom leads to uniform increase of head from zero to maximum head. Also, feeding from the bottom will cut the energy consumption and time by half if the same capacity pump is used (I think). You can prevent the backflow by putting a NRV in line.