there was several chiefs in the age of judges
Yes, during the centuries of the Judges and Kings. During Second Temple times there were Jews and non-Jews in Israel (Judea).
There is no one theme to the stories. Two recurring themes are Israel's unfaithfulness and God's faithfulness. In the book of Judges there are several recurring themes in the stories regarding the nation of Israel eg backsliding, oppression, repentance, deliverance
Deborah (Judges ch.4).see also:more about the Judgesmore about the Israelite prophets
Eli and Samuel were the last two judges of Israel before the era of the monarchy began.
No. During the times of the judges there were many cycles of backsliding, oppression, repentance and deliverance. God repeatedly raised up judges each time Israel began to take on the idolatrous practices of the people they failed to drive out of Canaan. Israel became oppressed by these Gentile nations when they repented and cried out to God, God delivered them through judges (military leaders) who over threw the oppressors.
Not all the Judges were men because one was Deborah.
The judges were sent, by God, to deliver Israel from their oppressors. The book of Judges is a repeating cycle of Israel turning away from God, then God allowing other nations to oppress Israel, then the people crying out to God for help, and God sending a judge to deliver them.
According to the Bible, the first named Moabite who goes into Israel is Ruth. However, it is highly unlikely that she was the first Moabite to enter Israel as the Moabites and Israelites had economic and political relations during the period of the Judges as well.
The seven-fold cycle of Israel consisted of Israel serving GOD, falling into sin and idolatry; being enslaved, crying out to GOD for help. A judge was raised up and Israel was delivered; cycle repeated.
Cycle of apostasy is the cycle of abandoning one's religious faith. During the Judges stage, God's people (Israel) were to live in a way that would bless the entire world (some refer to this as "wow-weird", following the 10 commandments would draw other nations to them and eventually into their religion, which would bless the whole world). Israel forgot God during the Judges stage and failed to drive out all the Canaanites, which began the cycle of apostasy. Since they failed to do this, God let them experience covenant-curses, but when they cried out, he sent them deliverers (judges).
Deborah was judging Israel during that time (Judges 4:4). According to the Bible, Sisera was killed by Jael, Heber's wife, after letting Him go to sleep deeply (Judges 4:21). After that, Jael met Barak and showed Sisera dead in her tent.