Is it possible to add up DC DC converters in series to create 36V output from 5V input?
This is possible only if the DC/DC converters are of the isolated kind. In an isolated converter there is no ohmic connection (no d.c. current path) from the output to the input. If you try this with non-isolated converters you will probably destroy them.

I can't say whether your plan is the best way to get 36V from 5V. I suspect you would get better efficiency from a single converter but I don't have a particular part to recommend.