[OT] A variety of terminology/history questions

Hi list! 

Me again. 

I've been working on some game stuff. I've also been doing some reading.
This has left me with a variety of questions which someone or some
several someones of this list can undoubtedly answer authoritatively (we
have all kinds aboard). So, with that in mind, I submit these questions:

1) USMC (or US military in general): What ranks are accorded the title
"sir"? This seems like an odd question except that I think the US
military differs notably from British traditions here. IIRC, in Canadian
tradition, an officer (carrying a commission from the Queen) is called
"sir". Non-commissioned members are not. Generally, if you call a
Sergeant "sir" here, you get a lecture about how he works for a living
and not on his knees. There are certain rare occasions where it might be
okay to call a Canadian NCO "Sir" (I believe some officers holding a
Warrant from the Queen find this acceptable) but there aren't many
cases. From a lot of the Hollywood products I've seen, I've seen people
calling NCO D.I.s and other senior non-coms in US forces "sir". What
actually is the US tradition in this regard?

2) Cavalry soldiers are called "troopers". Cavalry forms themselves into
"troops". What organizational level is a troop equivalent to
(Platoon/Company/Battalion)?  Does "Squadron" enter into the picture or
is that uniquely a UK/Canada armoured organizational element? Where does
it fit? (Platoon/Company/Battalion)? 

3) Do mobile (mechanized or armoured) infantry or cavalry scout
formations tend to orient their squad breakdown around vehicular
capacities? Or do they tend to retain squad or section breakdowns around
some administrative or doctrinal vision and then just divide the squads
out between vehicles? This latter situation seems less ideal (having
half of a squad potentially far from another half) but the former
situation seems to restrict your doctrine somewhat. How does this tend
to be done? And if the type of vehicle (and hence capacity) changes,
does unit section/squad organization similarly get changed? This all has
implications for logistics and long distance transport as well as how
mobile combat ops get executed. 

4) (USMC) Marines are "Marines", not "Soldiers". Soldiers are Army. I
know Marines refer to the Army (or have) as "Doggies" (or <expletive>
Doggies). I have heard Army soldiers called "Dog Soldiers" before. Where
did this term originate? Is there a historical antecedent? Is it still
true (that Marines refer to Army this way)? 

5) What is the common ratio of mechanics/motor pool techs/vehicle repair
techs/etc. to vehicles in a modern force? If I have a tank platoon of 4
tanks, or a tank company of 16 or 17, how many mechanics are likely
directly required in support of independent operations of this force? At
what level are such support services attached (Battalion or Brigade
level)? Is vehicle recovery part of the same support unit? Or is that a
separate organizational unit?

6) (USMC) "Every Marine is a Rifleman". Is this still true? Does it
apply to Marine Aviators etc. too? 

7) (USMC) Does the Marine corps still use Navy Doctors and Corpsmen? Or
do they have integral marine medics or life-savers?

These are only getting me started. But it'd be a help if people who were
"in the know" could answer some of these. I'm developing TO&Es for a
number of GZGverse forces, and some of this will help.