I designed a DC-DC converter once.[1] This is an exotic application - providing 60mA Teletype signals at up to 120VDC, with power from a 5V USB port.
There are two main trouble spots in DC-DC converter design - protection and noise.
A switching power supply is a dead short across its input once the inductor has saturated. The switch, usually a power MOSFET, needs to turn off on every cycle before that happens. Otherwise, something will fail and probably burn out. Also, the failure mode of power MOSFETS is usually "on". So protection circuitry is needed. Fuses, current limiters, etc. This is why UL approval for switchers connected to the power line is important.
Switchers work by generating big inductive spikes. Those spikes are supposed to be directed into capacitors and smoothed out into DC. Without suitable filtering, spikes will be pushed into the power source, the load, and the RF spectrum. A few ferrite beads, Zener diodes, and small capacitors in the right spots will fix this. LTSpice simulation is useful in picking the component values. You're not done until both the current and voltage curves are flat.
I am using "Switching Power Supply Design" from Pressman, Billings and Morey and "Switmode Power Supply Handbook" from Billings and Morey.
Both are excellent resources and look at design from a bit different point of view.
I think the biggest problems with swithing designs are not what you have listed, although both noise and failure modes are a huge problem and main cause of concern (and cost) when certifying your designs.
The biggest problem is that they are just so damn complex and they have so damn complex characteristics over time and operating parameters. You might think you understand how a switching PSU works but that's just an illusion. There are people who spent their entire life specialising in switching PSU design and are still learning. At best we can understand how they behave within certain parameters and then try to make sure to shut it down safely when we leave those parameters.
There are two main trouble spots in DC-DC converter design - protection and noise.
A switching power supply is a dead short across its input once the inductor has saturated. The switch, usually a power MOSFET, needs to turn off on every cycle before that happens. Otherwise, something will fail and probably burn out. Also, the failure mode of power MOSFETS is usually "on". So protection circuitry is needed. Fuses, current limiters, etc. This is why UL approval for switchers connected to the power line is important.
Switchers work by generating big inductive spikes. Those spikes are supposed to be directed into capacitors and smoothed out into DC. Without suitable filtering, spikes will be pushed into the power source, the load, and the RF spectrum. A few ferrite beads, Zener diodes, and small capacitors in the right spots will fix this. LTSpice simulation is useful in picking the component values. You're not done until both the current and voltage curves are flat.
[1] https://github.com/John-Nagle/ttyloopdriver