Thermochemistry: forms of energy & pressure
1.Does pressure decrease with time?


The ideal gas law tells us that
$$PV=nRT$$
or 
$$\mathrm{P=\frac{[nRT]}{[V]}}$$

If the temperature, number of moles or volume does not change, then the pressure will not change.  


  If pressure is caused by the force of gas molecules hitting the inside
  surface of a container, don't they transfer energy and eventually slow
  down enough to totally reduce pressure?


Yes, that's correct.  If energy is transferred out of the system, then the temperature will fall and the pressure will decrease.  But if everything is already at the same temperature, there will be no energy flow in or out and the pressure will remain constant.


  after the pressure is created, doesn't it require continuous energy to
  maintain pressure against a constant force


No, there is no requirement that energy must be supplied to maintain the pressure.  Again, if the gas, the vessel and the surroundings are all at the same temperature the pressure will not change.  However, if the entire system is not at thermal equilibrium, then heat will flow so as to put things at equilibrium and the temperature will change.