Guzu Yogore stared at the strange person glowering at him. "Do I know

  ^ "slowpoke dirt", huh?
 

"Your turn'll be next, Shirazu. See you in school!" Ukyo said
threateningly, then quickly slipped out of sight.

So Ukyou even adopts the same modus operandi?  Why?  Does she think
this is an effective means of confronting them, or does she think
that all these sixteen-year-olds really knew what was going on?

This was another one hour fic, inspired by a certain fanfic cliche.
Multitudes of fics postulate Genma as having made zillions of fiancee
arrangements for Ranma as a child, even though he only did this *once*

Well... twice.  Don't forget the Chardins.

in the original series (and that was clearly Ukyo's father's idea) and
it's rather unbelievable that hordes of parents would be 
eager to engage
their daughters to the son of someone as disreputable-looking 
as Genma.

So why has the same sort of thing never been applied to Mr. Kuonji?

Well... Mr Kuonji had a limited supply of Okonomiyaki carts, for one?

Well, now it has.

You could actually make a second or third arrangement for Ukyou very
plausible, as a rebound arrangement by a father who thought the Saotomes
were gone for good.  Use the "Ukyou's father was dying and he's concerned
for her upbringing" idea, or, better yet, he thought he was, but survived.