The origin of the "first" knights of Europe can arguably be found in the late 10th century aristocratic circles. With evidence of a distinguished class of aristocrats or clergy adhering to a set of understood virtues going back to the Roman Period. Authors like George Duby, Thomas N. Bisson, Stephen Jaegar, and David Crouch all convey their findings in books and articles on the subject.

Duby took the rise of the knight class to be a defining characteristic of the transition of power in this period. Where Bisson saw the crisis of multiplied castles and unmobilized knights in quest for more power, Duby saw the invention of the privileged hereditary knight class as the culprit. Duby saw the expansion of vassalage as a re-division of powers in the realm. The web work of political ties and fealty provided a challenge to rulers attempting to keep and consolidate power. In an age where ties, bonds, and oaths were rife- military and court service strengthened these bonds. From this arose the knight as a privileged social class, a privileged noble. I believe Bisson might see this as the beginning of the transition where administration of the realm equated to public order and power when the designation of official titles grew. As people on their quest for power saw the titles being bestowed, the chance for the designation as a knight was a high honor and cemented your position of power above others.

For knights as a military class and military information I would look in to the military orders, like the Knights Templar. Originating around 1120. Evelyn Lord's fairly recent work The Knights Templar in Britain gives a good overview of what they looked like according to the Templar Rule established at the Council of Troyes and their recognition under the Papal bulls issued by pope Innocent II. You have to keep in mind that the members of the Templar Knights were just as much monks as they were military men- this may not be exactly what you're looking for, but can give you a general start.

Clause 17 of the Templar Rule commands they wear white mantles and cloaks "to show that they had come from the darkness of evil to the light of purity." The addition of the red cross to the robes came later around 1145-53. The sergeants of the order- who were not full brothers or had taken full vows wore black surcoats, with brown or black mantles. The sergeants (probably) looked like your more run of the mill knights at the time. Knights and sergeants were told to keep short hair, but not shave their beards. Templar arms and armour changed as technology and fashions in armaments changed. Early knights wore a hauberk or coat of mail, with a white surcoat over this, and a padded leather jerkin underneath, chain mail hose covering the legs and iron shoes, and a conical helmet. They carried a shield, lance, and a turkish mace, and were equipped for the campaign with three knives- a dagger, a bread knife, and a pocket knife. The rule describes the black and white templar banner, the beausant or piebald banner. The banner was extremely important in their campaigns and served as a rallying point. -From Evelyn Lord's book

sources

The Knights Templar in Britain- Evelyn Lord

Thomas Bisson, The Crisis of the Twelfth Century: Power, Lordship, and the Origins European Government (2010)

Georges Duby, “The Nobility in Eleventh- and Twelfth-Century Mâconnais,” in Lordship and Community in Medieval Europe, ed. Cheyette (1968)

David Crouch, The Birth of Nobility: Constructing Aristocracy in England and France, 900-1300 (2005)

C. Stephen Jaeger, The Origins of Courtliness: Civilizing Trends and the Formation of Courtly Ideals, 939-1210 (1985)

edit: Also, I looked in to a book on my shelf by Alan Forey- The Military Orders... generally brother knights were given 3 horses to go on campaign with- 4 when there was an ample supply. Sergeant at arms had 1, 2 when ample. only knights had squires to assist them. He analyzes the language used to describe the differences in armor used. Instead of a hauberk, sergeants had haubergeon, which was probably shorter and lacked manicles protecting the hands; the chausses of the sergeants were to be withougt avant-pies covering the foot; and whereas knights wore either a helm or chapeau de fer, the sergeants only wore the latter, which was lighter and did not protect the whole head.