Things to avoid when using voltage regulators?
The problem of having multiple voltages to different parts of design has been solved by electronics industry with so-called multi-channel PMIC - Power management IC. Here is an example from Allegro A4490:



Or Texas Instruments TPS65400:



Here is an example (from my junk box) of how the power distribution block looks in reality (Proscan 4K 40" TV), using RT6914 PMIC:



This is a fairly common solution for many classes of devices: tablet/phones, TY-sets, set-top boxes, computer monitors, you name it. This is the standard technique.

Obviously a hybrid power topology is used, some regulators are in series, some are from parallel multi-channel PMIC. It should be remembered that the power-on and power-off sequencing usually has certain timing requirements, and a all-in-one single-IC PMIC has easier means to control the sequence. 

Overall the topology of regulators depends on required amperage of each rail. If you need 9V@100mA and 3.3V@5A, it is uneconomical to make 9V@3A regulator before the 3.3V one (I assume switchers, even if smaller Vout/Vin ratio is somewhat more efficient). If you have a bunch of low-current consumers at low voltages while, say, the main power goes to 5V rail, then it is perfectly fine to have the other regulators fed from 5V rail. An example could be the "hybrid" power architecture of Intel ATOM SoC platform, Powering SoC.