Question 1: Yes, in edit email select segment by in the right hand column and choose the segmentation you want to use. Then drag the objects from the top half of the list you want to make dynamic by segment down to the segment area. Once you do that you can change the value for that object for each slice of the segmentation
Question 2: Yes, in the form you can specify what to do for know leads and unkown leads at the setup tab
Question 3: No, I don't think this is the best way to do it. You should be able to reuse forms at the least and thank you pages and landing pages potentially depending on the use case. I would try to reuse as much as possible based on your reporting needs.