I am new to Joomla and I am trying to create a form system whose questions will change depending on what was previously answered. The idea is to store this data into a database and allow other users to comment on this form/post...so basically it's a form/forum hybrid. Is there any plugin or plugins that could help me with this? I am playing around with Fabrik but I am not entirely sure it's gonna work as it should.
The short answer is: you will need the assistance of a Joomla Programmer as it's highly improbable you'll find a plug-in that suits your requirements.
First of all, I think what you are looking for is properly called an 'adaptive survey' or 'adaptive questionnaire,' (not be confused with 'responsive/adaptive as pertaining to screen-size - so even Googling this will return some 'red herrings' and you'll find solutions that 'adapt to screen-size'...not exactly what you're looking for!) - in other words, you need questionnaire in which the next set of questions in the survey is conditional on the answers to the prior question (Note that there is some debate as to what to call such questionnaires) - but back in 2000, when designing online contest entry forms - we called these 'adaptive questionnaires.' In anycase, the diagram at that link will be helpful to you in describing what you mean by an 'adaptive form.'
Now, if your requirements were to stop here (you simply need an adaptive questionnaire), you might find something in the Joomla Extension Directory, but since you add another 2 requirements (at least), to pull it off you will require a bespoke solution. For example,
Additional Requirement: Once submitted, you want the answers to appear somewhere on the site (this is not typical); and
Additional Requirement: You will need commenting system for those answers.
Tying all that together will require some custom programming.