- What is the difference between 間 and ながら? Doesn't ながら just mean "while" while 間 can also mean "during"?
- どんなに ~ても and いくら ~ても both mean "no matter how". Are they interchangeable or not?
- Also, how is saying 最中 different from just using the ている form of a verb?
I think you are right. For example, テレビを見ながら食事する(I eat foods while watching the TV.) , 冬の間、亀は冬眠する。(turtles hibernate during winter.).
いくら ~ても(でも) is used with pronoun, adjective, and verb. どんなに～ても is used with adjective and verb but with pronoun is unnatural like どんなに私でも. So they are interchangeable except pronoun.
verb + ている means progressive like I am reading the book(私は本を読んでいます) and ～している最中 means "in the act of" and "be engaged on" like I am in the act of reading the book(私は本を読んでいる最中です。). They are same meaning, aren't they?