Note 1: (yeomanry)
The American Heritage Dictionary defines yeoman as: A farmer who cultivates his own land, especially a member of a former class of small freeholding farmers in England. Freehold is defined as: An estate held in fee or for life.
From the Encyclopeadia Britannica Online:
In English history, the yeomanry were a class intermediate between the gentry and the labourers; a yeoman was usually a landholder but could also be a retainer, guard, attendant, or subordinate official. The word appears in Middle English as yemen, or yoman, and is perhaps a contraction of yeng man or yong man, meaning young man, or attendant. Geoffrey Chaucer's Canterbury Tales (late 14th century) depicts a yeoman who is a forester and a retainer. Most yeomen of the later Middle Ages were probably occupied in cultivating the land; Raphael Holinshed, in his Chronicles (1577), described them as having free land worth £6 (originally 40 shillings) annually and as not being entitled to bear arms.
In England upon the former manors, farmers (the original meaning of the term was leaseholder or rent payer), who held land under long-term leases, gradually replaced copyholders, or tenants subject only to feudal dues. These farmers constituted the free English yeomanry, and their appearance marks the demise of the last vestiges of medieval serfdom.
Note 2: (misfortune of your birth)
The misfortune of Harriet's birth refers to her illigitamate beginnings.
Note 3: (me)
The improper use of "me" (instead of the proper, "I" ) in this sentence is very likely intetional and an example of the way Jane Austen draws her characters. Harriet is talking of the quality of her education, and demonstrates it by making this error.