FFF
Re your first query, the tailplane is responsible for producing longitudinal stability. If you give it a smaller arm by moving the CG aft it is less efficient and so a slightly smaller elevator input will be needed to reach the stall (or, if you prefer, pilots have to overcome stability when controlling an aircraft – less stability means less control needed to achieve any manoeuvre – in this case a stall)
As to your second query, moving the CG forward makes an aeroplane more stable, so more downforce is needed at the tail (to stop the nose going down) this “downwards lift” makes the aircraft appear a bit heavier to the wings and so the stalling speed goes up a tad.