Hi,
It's not clear to me what exactly you need.
When you talk about an isolated supply, then I expect informations like:
* input voltage (range)
* isolation voltage
* output1 voltage
* output1 current
* (voltage and current for other outputs)
* total power
Then I'd go to a distributor or DCDC converter manufacturer and look for matching devices.
For sure you are free to design your own DCDC converter.
This is a question of: effort, cost, volume, electrical parameters (like drift and noise...), other ideas
We can't answer questions about effort, cost ...
So I'd rather like to ask you where you see the benefit in designing your own.
Or the other way round: When you see the ready to buy DCDC converters, what don't you like on them?
Klaus