Your approach can work. It has the advantage of using less expensive components (rather than a bulky coil). Your eggs are not all in one basket (as they are with one big coil).
And if something goes wrong you have replacement components, and you will know how to fix it. This is crucial if we have societal meltdown.
* One technique not mentioned yet is switched capacitors. It will not necessarily be easier to construct than the voltage drop method you have discussed. However it has efficiency on its side (and elegance). Connect a stack of capacitors in series. Charge them quickly to 400V. Then switch them so they are in parallel. This divides the initial charge by the number of capacitors.
That's the theory anyway. It has problems of its own. It will require massive capacitors. One bad capacitor can mess things up.
I plan to build three 'drop modules' that each have a power fet in parallel with 3 50W 24V zeners.
As you may know, it is problematic to parallel heavy loads. One of the devices can have slightly different characteristics. As a result it could hog excessive current. It could burn up prematurely. Thus it is wise to install a load-balancing resistor at each dropping device. These can be very low ohms.
* It appears you wish to find a way to make a voltage regulator, compatible with the high V source. There are mosfets/transistors rated for that high a voltage, and which could endure the heat. It would require a bias circuit which likewise is compatible with high V. It could be made to automatically fine-tune itself so that the load always gets 13 V. You might even get by with just one large dropping device, rather than having to parallel zeners, etc.
This link (tpub.com website) may provide ideas:
https://www.tpub.com/neets/book7/27k.htm
Re-reading your OP, this looks the same as your Idea #3. Please disregard this if you've already decided it's infeasible.