Questions & Checklist setup

I've personally done this lot's of different ways so I'll try do my best to explain how I might look at it. 

Can you confirm - the Question and Sub-Questions table are children to your checklist correct? So when you pick the checklist on the Product, you are then planning on creating tasks for each question? What then it the Template Table for? 

To try and answer your questions though with what information I have: 

1. This is the trickiest. One option is to rethink the idea of the 'primary key' on your table when you create a task. So for example - lets say you Product Record ID#1, and you're copying over Question #5. Your would set the key field of the Task to be '1-5' as one example, the join between Project and Question as the string. The idea behind it then - is that if you can build the idea of predecessors using that logic where all of your tasks tie back to the original question. So - if you know that Question 5 is the predecessor to question 6 - then you know in your 'Tasks' you're looking for the Task record with key '1-6'. It's a backend way to never stray very far from the original template. The drawback to this is that its typically harder to make on demand items. This key structure revolves around the initial load so manually creating new ones is a little tricky. 

The other option I've seen work well is to use Quickbase predecessor fields in your template and then when you create your tasks - to user formula queries to update what the 'task' equivalents are. The native predecessor field will tie a record to one or more Record IDs in that same table. When you create a task from a question record that has a predecessor - you can reconstruct a formula query that looks at the lookup predecessor value from the question - and splits out to search for all the tasks where the Related Question is listed in the predecessor. You can then make an update to the task to merge what the new Task predecessors would be. This is easier than the first suggestion but doesn't always provide the best visibility depending on your opinion of QB predecessor fields. 

2. Are you asking how to create sub-questions against a product similar to how you have Questions/Sub-Questions? If you're using the checklist/question/sub-question as a template that you then pick on a Product to do a Product/Task structure - then you need to mirror the idea of SubTasks underneath tasks. When using this kind of template model in QB you need to match the structure where ever you're loading this template to

3. This will depend on how your users are completing this items. If they're editing through a 'form' - then the easiest is to have a 'entry type' field in the question that you fill out with Number, text etc. Then on the form, you use a form rule on the task where you show/hide the right field type based on the template type that you set. This works for simple types like numbers and basic text, when you get into dropdown values - you will need to think about building out some kind of Master Dropdown table that contains all potential dropdown options across any question. Then you do a conditional dropdown in your task to make sure you're showing the right responses based on the question.