"and actually shaken hands with her at last..."See in text(Volume I - Chapter III)
In his edition of Austen's works (Oxford University Press), R. W. Chapman noted that, at this point in the 19th century, shaking hands was a "mark of intimacy or affability." Clearly, Emma is a bit surprised and flattered by Miss Woodhouse's gesture.
"make up a card-table..."See in text(Volume I - Chapter III)
This is a phrase meaning that Emma could not find enough friends for Mr. Knightley to play cards with; for example, she could not find three other friends to make a foursome for partnered card games.
"Were not you struck..."See in text(Volume I - Chapter IV)
In other words, the phrase "Were not you struck?" asks, "Did you not notice Mr. Martin's strange behavior?" Harriet does not believe Mr. Martin is a real gentleman.
By "aloat" Emma means that Mr. Martin's share in the family property is inaccessible. In this case, he is invested in the lands and animals of the family farm.