- Would it be appropriate for people not in the family of a person that died to be in mourning dress?
- rules were not as solidified as in later 19th cent. And were fluid based on social level. Court mourning also had to be taken into account.

- Would soldiers be allowed to be out of their uniforms if not on duty? Or at a costume party?
Navy officers - not onshore - pressing - Austen/Mt. Mansfield: “"William had obtained a ten days’ leave of absence, to be given to Northamptonshire, and was coming, the happiest of lieutenants, because the latest made, to shew his happiness and describe his uniform.
He came; and he would have been delighted to shew his uniform there too, had not cruel custom prohibited its appearance except on duty.
So the uniform remained at Portsmouth, and Edmund conjectured that before Fanny had any chance of seeing it, all its own freshness and all the freshness of its wearer’s feelings must be worn away."

Army has full dress and undress. 
the Duchess of Richmond's daughter describes how the gentleman left the ball on the eve of Waterloo in such a hurry that some did not change out of evening dress.

Other re: military: Army- costs and ranks: https://www.wattpad.com/404805892-reading-the-regency-gentlemen%27s-occupations-army/page/3

Army - http://homepages.ihug.co.nz/~awoodley/regency/army.html

- What would a constable or policeman wear in this time?
https://regencyredingote.wordpress.com/2011/03/04/the-regency-had-no-crime/
Refers to the 1901 “A History of Police in England” (Note: late 19th/early 20th century ‘histories’ must always be slightly suspect as they tend to rely on hearsay, traditions, and a bit of a “see how much better we are now” attitude. Not saying this one is like that, just a caution.)
https://books.google.com/books?id=7rgXAAAAYAAJ&printsec=frontcover&dq=a+history+of+police+in+england&hl=en&ei=a3BkTYaIA4rVgQeRo5H6AQ&sa=X&oi=book_result&ct=result#v=onepage&q&f=false

Various Bow Street groups (Runners - detectives) - 1753 - no uniform but they did carry a 
Bow Street Horse Patrol - 1805 - leather hats, blue coats with brass buttons, blue trousers, boots
London Marine Police Force - 
The Metropolitan Police Force was not established until 1829

Also fun is the description and image of the Bow Street Office in Ackermann’s “Microcosm of London” Vol 1.
https://books.google.com/books?id=LtUgAAAAMAAJ&printsec=frontcover&source=gbs_book_other_versions_r&cad=3_0#v=onepage&q=robin%20redbreasts&f=false

- Did older generations tend to follow fashions to a degree or stick with the popular fashion of their own day?

-What would be an appropriate range of ranking officers to engage socially together?
Consider Lady Catherine’s comments on Lizzie B’s status, as well as her retort.