bloki

Resistor wattage is always added together. No matters is it series or parallel connection.

You may use computer PS as it is or modify it.

Comparing both regulators 1083 and 338 regarding ripple rejection parameter you can find that both has the same guaranteed value, -60dB. And it defines how much ripple you will have on output voltage. Some types of linear regulators can oscillate if output capacitor has very low ESR.

You can make such inductor. core diameter=50mm coil length=50mm coil depth=40mm wire diameter=0.5mm wire length=2500m number of turns=9000 wire resistance=216ohms Use CALCOIL program which can be downloaded here: http://www.elektroda.net/download/file654.html

You may connect 4.6H inductor if it can withstand at least 200mA current and 2.2uF/250Vrms (rms not DC, DC rating should be 630V)capacitor parallely to mains voltage.

Yes each signal has it's own carrier frequency. Such system is called FDM or Frequency Division Multiplex.