I like your pronunciation a lot, but I would spell it Hyakinthus or Hyakinthos or whatever best approximates the Greek name, rather than
Hyacinthus. Lately I've been mad into
Jacinto, but that's just by the by.
The only name that sounds like
Hyacinthus to me is
Hiawatha.
And
Lindy is neat as a boy's nickname. I think
Linden is the obvious choice--this used to be a big favorite of mine (still is, really), but I never thought of a nn for it.
Lindy could also work for
Lyndon, Lindall, Lindell, Lindsay/Lindsey, or
Lynn.