Hi Walt,
To try to help in answering your questions (hopefully correctly

)
from what I have read and learned over the years is:
There are several reasons the Harley name came first,some say he had great ideas in forming the MOCO and the Davidson brothers wanted to honnor Mr.Harley, other ideas say they tried it both ways and going with H-D rolled off the tongue better.
As far as the tires go that has changed over the years some due to design improvements and some due to styling. I am by no means an expert but if you look at the very early bikes like the 1903 era I believe the front and rear tires are the same. Over time the HP and speeds increased as well as an interest in better cornering. Motorcycle tires usually have several more forces applied to them vs. car tires due to leaning as well as more HP to weight. I can envision wanting larger rear tires to increase traction, soften the ride and increased braking somewhat, going too large could affect leaning though. I would think a thinner front tire would make the steering feel lighter and to many look better,same idea as larger rims yet if the sidewalls on either front or rear is decreased too much the ride will get harsher due to less ability to absorb impacts. Some people like the more stable feel of a wider front tire so some bikes come with it like the Fatboy and many touring bikes.
As far as the gas gauge I would have to guess it's harder to work with a smaller amount of gas (compaired to a car) that is very seldom level. I don't know how inaccurate a Harley gauge would be compaired to another brand of bike though?
With the kickstand being called a Jiffy Stand I have read where it was an advertising thing saying "this stand could be used in a jiffy" or in our language of today it could be used quicker than the first stands which were hoops that were more like centerstands which came down from the rear fender area and you had to lift the rear of the bike and get the rear tire off the ground to use.
I would imagine that the reason for the left side use of the stand would be because most early riders and passengers learned to get on a bike the same way they got on a horse which would be from the same side. It is also easier for most people to get off on the low side.(No pun intended) Some police departments train their motor officers to get off on the high side as a safety thing so on a traffic stop they will not get off and step backwards into traffic.
Maybe some site experts or someone from the MOCO will post sometime to verify or correct me?