Note 1: (box'd)
Here is a strange use of an apostrophe. The use of it here, and not in other situations, perhaps suggests that the "ed" ending was regularly pronounced more distinctly and seperately than it is today. Where we today would treat the word "boxed" as one-syllable, perhaps in Austen's day it would normaly have been pronounced as two: box-ed.
Note 2: (Court-Leet and Court-Baron)
"Leet" is a manor court where minor offences are tried, and baronial courts were similar. (According to the Dictionary of Phrase and Fable on the Bartleby website.)
It may be that this is an allusion to a specific book:
Kitchin, John. Jurisdictions, or the lawful authority of the Courts Leet, Courts Baron, Court of Marshalseyes, Court of Pypowder and Ancient Demesne. 1605. 4th ed. 1663. 1st ed. in French, undated, but c. 1579.