多小 is wrong, 多少 is correct.
I think chat gpt is right. 几 is more casual and often used in oral Chinese.
If you need to write an article, use 多少 is better, more formal.
(experience from student： If you ...
全力以赴 means put all your strength into it, that is, the last stand and there is no way out.
尽力而为 means to do one's best and to do it by one's own strength.
They all mean taking a positive approach to ...