Old Rules:
Design First Cap for 5% ripple.
The PT-Rectifier-1stCap loop must be Small and Fat. This loop is full of crap. Don't connect rest-of-circuit anywhere except AT 1st Cap.
Design each R-C filter for 30dB loss at 100/120Hz; i.e. around 3Hz poles. Trying for more per section leads to "too expensive" cap sizes. Also residual resistance limits how much reduction you can really get.
More R-C stages is better. It is usually the higher harmonics which are most annoying. More stages is a steeper roll-off.
A key design decision is raw DC to filtered DC voltage. Large resistors filter better but make large voltage drop. I recall a Heath which started with 500V at the power stage but dropped to 90V at the first preamp tube-- the many R-C stages made that first node clean even with "small" filter caps.
BUT: New Rules: cap prices have come way down over the decades. It may now be very reasonable to design for 2% and 1Hz. I would still keep the number of R-C stages high. While C-R-C may be ample for power amp push-pull driver, a phono preamp would normally want at least four R-C stages of filtering.
Motorboating can be a different issue. While limiting resistances may help, the real technique is to develop the forward gain, and derive the sneak-back path, and compare gain/loss. While "filtering" aims for reduction of 100Hz+, hi-fi amps with sub-20Hz response need capacitor "clamping" down below 1Hz. This does favor high-C low-R design, which is now economical.
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