as far as I can guess it's close to the second one here.
Maybe you're right.
なり in this case describes that there's an available way you can choose directly, but it seems that you are still able to choose another way.
- 「彼になり相談したらいい」 could be "You may ask him (or another person.)"
- 「電話なりしてください」 could be "Call me (or use another way to communicate with me)."
we have to think about fight preparations and the way to win.
This なり doesn't mean "and". If I translated this phrase, it would be...
we have to think about the way to win such as fight preparation.
Because なり denotes a specific example as I explained above.
FYI, if this phrase contained two なり like this:
戦う準備なり勝つ方法 なり を考えていかないといけないが…
This should be translated as
we have to think about fight preparations or the way to win (or other things we need).