I do not fully agree with 2, 3, and 4.

2 seems wrong in terms of efficiency. But you will not run into indexing errors with a foreach loop and your own code looks cleaner.

3: String interpolation with $ is the way to go nowadays.

4: I disagree. In most cases you know the type you are working with, so var is fine. With your logic it would be more readable to write an additional comment above every variable indicating its type. var is always a personal decision imho.