Wounding transformers is easy for high freqency.
An example of a transformer from an ATX power supply in the 300W range.
Runs at ~50kHz or so.
5V secondary is whole 3 turns IIRC. Times two because it's two diode rectifier.
Primary which has 170V square wave going through it is 20+20 turns (split to reduce leakage inductance).
So it's fairly easy to wind, even without experience.
I have wound my first switching power supply transformer without any experience whatsoever.
Just making photos and looking at how it was originally wound.
Transformer provides the separation, allowing all the rails to be independent.
Then by using the right amount of turns you get any output voltage you want.
AC voltage is square wave so it's easy to calculate all the secondary voltages (LC tank required).
If you insist on using only off-the-shelf parts then focus on non-isolated topologies.
Pretty much only inductors are used.
Look up Texas Instruments "power topologies handbook".
https://www.ti.com/seclit/ug/slyu036/slyu036.pdfBoost to 15V and from there you may try buck and Inverting Buck-Boost for all the voltages.