In say, 14th-15th century France or England, would a typical knight own a castle? If not, what rank of noble would you usually need to be before it was normal to have a castle?
If a knight didn't live in a castle, what would his house be like? Did all knights have their own homes, or did some of them live with nobles of higher rank?
How many people and of what rank would you expect to live in or around a single castle? How many people would a typical knight have authority over? Of those, how many would be 'men at arms'?
Also, does anyone have a rough idea of what percentage of a medieval knight's (or indeed any other feudal noble) total wealth would be in their personal arms, armour, warhorses, etc. vs. property? Would they have any other significant wealth, such as cash, investments, shares in business?
In France, the typical castle was owned by a knight (A Seigneur). These were generally small village castles, nowhere near as grand as the castles owned by Kings or Great nobles, but there were many of them (one in every village in some parts of France).
Not all knights owned castles, however. Many knights were 'household knights' who were landless (or did not have enough land to support a castle) and were supported (paid) by the king, or some other lord.
In England, knights were originally supported by a 'manor' (land and people - circa 300-350 people per manor at the time of the Domesday Book). The knight might have a castle on his manor, but this would be more likely in the 11th - 13th century, and becoming less likely by the 14th and 15th century. The knight might more likely have a manor house than a castle. Many of the wooden motte and bailey castles built by Norman knights on their manors after the conquest were never replaced by stone fortifications. They were often replaced by a manor house instead.
England was more peaceful than France, and the number of castles had declined since the early centuries after the Norman conquest.
In England, many of the nobility would have castles, but there were only about 10-20 Earls and 200 Barons at any one time in England during the Middle Ages. Some nobles would have multiple castles, especially in dangerous areas such as the Welsh Marches. Some of these castles would be commanded by a knight (but not owned by the knight).
For example, here are some of the garrisons for important castles guarding the Welsh Marches in about 1160 (a little earlier than the period you are looking for).
The Pipe roll entries show that Oswestry Castle had a garrison of one knight, two porters and two watchmen between 1160 and 1165 (William Fitz Alan was the lord of the castle, but he was a young child and was a ward of the king. The King appointed Guy Lestrange to administer the Fitz Alan lands, and this is the garrison which Lestrange paid for as shown in his accounts of his guardianship).
The two other Fitz Alan Welsh border castles of Clun and Ruthin seem to have had the same peacetime garrison of 5 men. Both were commanded by a knight.
A higher percentage of English castles were Royal castles or the castles of nobility, rather than knights castles.
In England, even more than France, during the 14th and 15th centuries, the feudal levy was becoming less important as a source for armies, and paid knights and household knights more important. Land holding knights were more and more likely to pay a fee, rather than render "knights service" in person.