Here is a list of mods I made at RPGWatch, hopefully all the links still work.

This page, is the center of what little Mod activity there is on the web, these are the Holowan team whom have done most of big KotOR 1 & 2 Mods.
http://www.lucasforums.com/showthread.php?t=177647

Stoffe has a very nice ReSkin of Jen-Zi

Pecoes has made great new mod called Jade Empire in Style check out his video. The list of changes is to big! :)
Pecoes quote....
"I can say without the slightest bit of exaggeration that this is the largest mod for Jade Empire. In fact, it's many times larger than all other mods combined. This mod has gone beyond a few minor changes here and there. It has turned into a total overhaul."

The Jade Empire Wiki

Pecoes
Allow me to add another link! We just founded a new wiki to collect and consolidate all modding knowledge about this great game: The Jade Empire Modding Wiki

Here is Tk-102 Save Game Editor, you may have to right click.
http://www.starwarsknights.com/forumdl/jse_05.zip

Here is a fix for the gay relationships so now we can play as a female and romance both Dawn Star and Silk Fox if I understand this post correctly. Edited in the two Romance-able Females Dawn Star and Silk Fox.
http://www.lucasforums.com/showpost.php?p=2401203&postcount=173

Here is a Mod pack by papagamer which includes several additions, a list follows.
http://www.papagamer.com/files/je_papagamer_mods.7z
\extra styles
Adds five combat styles to your character after the training bout with
Jing Woo. You must start a new game to gain the additional styles. The
styles added are:
* Rhino Demon (Trans): Rhino Demon transformation as added by the pre-order "bonus" CD
* Monkey Paw (Martial): strong and fast Martial style
* Saber (Weapon): single broadsword like the pirates use, equivalent to longsword
* Two Hammers (Weapon): two spiked maces, strong and slow
* Death's Hand (Weapon): two black-bladed broadswords as used by DH; style consumes
no Focus and can damage spirits; HUGE Power Attack that covers a lot of distance;
originally you could only upgrade Damage—added Chi Damage and Speed upgrades; but,
these have not been tested

\level faster
Reduces the experience points needed to achieve each level. You will
level up faster and top out at a higher level.

\reveal map
Removes the "fog of war" that obscures the maps in each area.

\tiens justice
Replaces the Demon Staff model with Tien's Justice model (the spade
staff originally used in the Limited Edition of JE on the Xbox). All
the stats are the same, you just get a different staff model, name
and description. You'll find the Demon Staff/Tien's Justice in a
pile of bones near the Unfinished Tomb in Necropolis.

You don't really need any other mod than Jade Empire in Style since it includes a lot of other mods, and those that are not included are probably going to break the mod. And yes, it includes the gay kissing fix.

http://jade-empire-in-style.com/ - for ease of use for those who don't want to search around for the website :)

Speaking of mods, would any be recommended for a first playthrough, or should one start Vanilla first?

Jade Empire In Style breaks a few things as I recall, and nothing else is that game-changing. Use the fix for gay relationships if you want, otherwise there's a couple other player-character retextures out there, I think. I like Jen Zi, myself, so I haven't kept track of where. In any case those are preference-based, of course.

Playing with the 'Jade Empire in Style' mod and ran in to a problem with a fight not ending fairly early on. Found a fix for it here:

Seems I'm unable to post links at the moment, so for anyone looking it can be found in the mod's forums. Problems section, 'Fights that don't end 2' thread.

Seems like that may be the last update that file got, so hopefully there's no other issues like that.

Not sure what you mean or why this is necessary, I have this link in the first post.

Whoops. I didn't see the url in the link when I first looked at it.

Is Jade Empire in Style safe? Cause I went to the site and it says "Not secure"

The site certificate is probably expired. Download it as see.

Do you mean "Safe?"

Is there a mod that prevents the game from crashing in the Level Up screen?

Hopefully someday there is some Community bugfix for the game of sorts to deal with any remaining bugs.

I heard that there are even endings that are bugged and do not appear.

Good game nevertheless. A shame Jade Empire 2 did not happen and likely never will.