Just use the Cloze code as an example. "I'm working with more complex question types (self customized) than it can handle" Perhaps the following project can help you Improving the multianswer(cloze) question, a proposal
I thought using the Description question type, as the main question body, and the subquestion that will be from customized type will use it's id in the parent field, is their something like this ?
The description type allows you to give all the infos necessary for a following group of questions. However there is no links between the questions ( i.e numerical data) other than the ones defined when you create the other questions. In a cloze question all the subquestions are defined at the same time so you can link the data but the questions cannot be changed from one student to the other unless you create many different cloze questions. You can create new question types that could use the parent field to retrieve data from the main question or from each others. The calculated question type allows to share parameters or data at the category level and can perhaps be used as an example for your work.