I don't agree much with your point 3. Before going to string theory, you should consider an intermediate step that we master well: quantum field theory. This unifies quantum mechanics, special relativity and field theory. From there, we can then move further. This could be string theories, or other stuff.
By the way, you may like a series I wrote on that topic 3 years ago (see here and all posts quoted at the end). This is inspired from this reference book which will be translated into English in 2021 (hopefully as this takes time and my time is limited).