Re: decoupling capacitor
coupling caps are usually needed if you power your source from the grid. if you have battery, you usually don't need any caps. that's how people avoid supply glitches in their circuits. however, the bad thing about battery is that they run out.
normally you would use umm .1uF to 1uF.
it acts as a smoothing function, ie any spikes from the supply would be directed to ground, instead of to your circuit (which may blow/destroy some of your ics up). So put a cap near the supply source connection, then another near your ic Vcc/Vdd.