Samurai do to sustain themselves economically? Did they rule over peasants or did they work alongside them?

A samurai who was retained by a lord would receive a stipend in koku, the amount of rice to feed someone for a year. Retainers in higher positions would receive more koku and thus be able to support more retainers of their own. This became a problem in the late Edo period when inflation resulted in stipends being worth less than what a peasant could make. At that time, samurai were not allowed to work and many gave up their status to become peasants so they could work to support themselves.

During the sengoku jidai, who was and wasn't a samurai was much less clear. It varied across time and province. The higher class called themselves bushi. Lower ranking samurai might be called goshi, jizamurai (literally land-samurai), or inakazamurai (country-samurai). They would work the land when not called into service for their lords. Peasants would be drafted, and the line between a peasant who knew how to use a spear and low-ranking samurai who farmed was often blurred. There was greater social mobility prior to Toyotomi Hideyoshi, who had been born a goshi but was raised up by Oda Nobunaga, and later decreed a much stricter caste system.

Where Would A Samurai Learn How To Fight?

Martial arts that were established before Japan modernized are now called koryu (literally, old-school or old-style). Unlike modern martial arts, koryu arts actually encompassed multiple disciplines. If you enrolled in a koryu school, you might learn to use a sword, naginata, spear, bow & arrow, and possibly some jujutsu. There are even ryu that include field-fortification and knot-tying. Many schools included weapons or subject matter that other didn't. Ogasawara-ryu, for example, includes mounted archery but heavily emphasizes etiquette. Muso Jikiden Eishin-ryu focuses on iaido (sword handling), with a little bit of partnered kata practice (bokken-on-bokken). Tendo-ryu focuses on naginata, but does include swordsmanship, and has become mostly practiced by women. There are even koryu schools that focus on shooting guns- hojutsu.

A kenjutsu dojo, in the sense of a dojo that only teaches kenjutsu, would have not been much of a thing until the Edo period, when koryu arts began discarding parts of their curriculum they considered obsolete. Kenjutsu remained popular among martial artists because swords were still carried as sidearms. It was later sword-focused styles that eventually evolved into modern kendo. Ono-ha Itto-ryu and Hokushin Itto-ryu both lent quite bit to kendo, but would have been very different from arts that were practiced during the sengoku jidai.

The average samurai did not enroll in one of these schools. They were more like academies for those that had a particular interest in honing their martial skillset. Certifications issued by the schools would help a samurai increase his income, but it was not expected that most would have certification. These certifications (menkyo) were scrolls that listed techniques the student was proficient in. Most lower ranking samurai would have trained in drills organized by whichever clan they were serving as preparations for going to war. Your lord is preparing for battle? You're going to be mustered, handed a spear, and told to practice battlefield drills. Not a whole lot of need for kenjutsu there. If samurai were so inclined, they might spar on their own time, and learn what they could from each other, but dedicating the time and tuition towards enrolling in a particular ryuha was not something most could do and wasn't all that useful on the battlefield. Oddly enough, during the Tokugawa period, membership in a ryuha became considered classy due to its association with the bushi and many peasants would enroll in any school that would take them merely for the prestige. They were not unlike country clubs.

Most famous samurai were not formally trained as part of these ryuha. Whatever training they received would have been part of their clan traditions and, as far as I know, those are mostly lost. The samurai who are remembered for being martial artists were atypical and often low-ranking: Tsukuhara Bokuden, Miyamoto Musashi, Muso Gonnosuke, Iiizasa Choisai. These people devoted their lives to martial arts and were known more for the arts they founded and their successes in duels rather than feats performed on the battlefield.

Koryu arts themselves are a fascinating subject. If you'd like to learn more, look into anything by Donn Draeger, Mike Skoss, or Ellis Amdur.

How would a samurai become a Ronin?

Lose retainership. If no one will give you a stipend to keep you around, you'd be a ronin. If your employer died or fired you, and you couldn't find another one, you were a ronin. If you decided to leave whatever position you held to go be a bandit or travel the country and challenge people to duels, you were a ronin. Not much more to it than unemployment.

What were the expectations for Samurai Women/Girls?

Today, samurai women are associated with the naginata. This would not have been the case in sengoku Japan. There are a few tales of women taking up arms, but in most cases their roles would have been somewhat analogous to ladies in medieval Europe. Poorer samurai women would have still had to work and be homemakers, while bushi women would have been more akin to noblewomen*, to be married off in various alliances.

• The nobility proper were a different class that had become rather insignificant by the sengoku jidai.