TS>1)  What exactly goes as far as 'allowed' in Ranma fanfics.  I'm told 
TS>that by convention, use of manga characters only is encouraged, if not 
TS>required.  Is that true?  Manga only?  If not, who's acceptable?  
TS>Hinako Ninomiya okay?

I've never heard of such a convention. I've also read tons
of Ranma fanfics that seem to be based on the anime
characters, not the manga characters. There are also some
fics which make mention of certain OAV episodes but also
draw roots from manga stories. I've also seen numerous
fics which have Hinako in them.

As far as I'm concerned, there's no such thing as a "manga-only" rule.

TS>2)  What is the spelling for the five yen trick Hinako-sensei does?

Happo go-yen satsu or something like that. Ask around some more...

TS>3)  Most of the characters in Ranma 1/2 have name-puns. Saotome being a 
TS>reference to "girl," etc.  How far does it go?  Does everyone's names 
TS>work as a pun?

I don't think so... I think Akane is a pretty normal name.
As for names, most of them have meanings. Ranma I think
means "Wild one" and Genma means "Black one." Kasumi
means something like mist or river, I'm not sure. Nabiki
has a meaning, but I forgot.

Then there's Ukyou, which is supposed to be a guy's name.

Ask around some more...

TS>4)  The fighting style that Ranma employs is supposed to be the 
TS>Anything-Goes Martial Arts style.  Then again, he also says he studies 
TS>kenpo.  I take it there are various forms incorporated in the AGMA style?

AGMA is the exclusive style of the Saotome and Tendo clans.
It seems to be a generic fighting style that uses hands and feet,
as well as several other weapons. It is also supposed to be
specialized in air combat.

However, according to the story, it is based on kenpo karate.
(or was it kempo?) AFAIK, that's what the AGMA is based on, 
and is the only traditional form incorporated into it. However, 
take note that Ranma learns a lot from Cologne and he considers 
these learned techniques as parts of his AGMA style.

Also, since Ranma and Genma were travelling all around China,
it is quite possible that they had learned and incorporated a
number of other Chinese forms into the AGMA.