What are the implications of "ve'Atah Sechezeh"?
Rashi: It means with Ru'ach ha'Kodesh. 1
Seforno: Yisro was telling Moshe that, although the adjudication could be performed by the judges,, choosing the judges is something that only he could perform.
The Mechilta writes similarly
What is the definition of "Anshei Chayil
Rashi: Men of wealth, who need not flatter (they do not need others' money), men of integrity, on whose word one can rely, and to whom one therefore listens and - who are impervious to threat.
Ramban #1, #2: Men who are capable of leading large groups of people or who are strong and competent 1 incorporating the other three Midos - men who are G-d-fearing, who love the truth and who detest extortion (dishonesty). 2
Rashbam: Men who are wealthy and powerful and who are not afraid of anybody, men of integrity and men who detest bribery and what is stolen. 3
Seforno: With four levels (incorporating "Yir'ei Elokim" and "Son'ei Batza") of judges, 4 litigants who were not satisfied with the first, would go to the second, from the second to the third and from the third to the fourth - with the result that very few litigants would need to come to Moshe, thereby lightening his burden. 5
Mechilta: "Anshei Chayil Men who are trustworthy
See Ramban's elaborate definition of the word "Chayil".
And obviously, men who are wise and learned, which went without saying (Ramban).
In Pasuk 25, the Seforno translates "Anshei Chayil" as 'Charutzim' (knowledgeable and diligent).
Which, as the Torah indicates in the next Pasuk, was the main objective of Yisro's advice.
Mechilta: And Yir'ei Elokim" are men who will carry out compromise in Din.
What is the meaning of "Son'ei Batza"?
Ramban #1 (citing R. Yehoshua in the Mechilta) and Targum Yonasan: They are loath to accept bribery. 3
Ramban #5: Refer to 18:21:2:2.
Mechilta: "Anshei Emes"
Ramban: This refers to property that is truly his, but others could take it in Din - he does not have a proof that he bought it. (Such a person hands it over voluntarily). The Mechilta implies not like this. Moshav Zekenim, Rosh
Why does the Torah say "Son'ei Batza", and not just 'Einam Mekablim Shochad'?
Why does the Torah begin the highest figure and progresses downwards - officers of a thousand to officers of ten?
Rashi and Targum Yonasan 1 (on Pasuk 25): Because as far as the number of officers is concerned, it begins from the least and progresses upwards - from six hundred officers of a thousand, six thousand officers of a hundred, twelve thousand officers of fifty and sixty thousand officers of ten. 2
Why are so many judges (almost ten percent of the population) required to judge the people?
Oznayim la'Torah: Let alone the generation of Moshe
See Oznayim la'Torah for more detains.
What is the significance of the fact that Yisro listed four categories of people and four groups of judges?
Oznayim la'Torah: It seems that the twolists are interconnected
It already says "Yir'ei Elokim." Surely they are truthful
Moshav Zekenim: They get the correct Halachah. Beis Shamai and Abaye were Yir'ei Elokim, but [usually] the Halachah is not like them against Beis Hillel and it is like Rava against Abaye.
QUESTIONS ON RASHI
Rashi writes that there were 600 officers of 1000, 6000 officers of 100, 12,000 officers of 50. This adds to 18,600; less than 600,000 Yisraelim remained. Why were there 60,000 officers of 10?
Da'as Zekenim #1: First they appointed 60,000 officers of 10, and from the 60,000 they choose 12,000 officers of 50, and from them 6000 officers of 100, and from them 600 officers of 1000. 1 2., Hadar Zekenim #1, Riva: The judges were not among the count of 600,000, for they were above 60 years old (or from Shevet Levi - Moshav Zekenim citing R. Yeshayah). Da'as Zekenim #2
Da'as Zekenim, Riva: It says in Sanhedrin (18a) that there were 78,600 officers! This counts titles (i.e. a single judge can be counted up to four times, of he was a judge over 1000, 100, 50 and 10).