Since multifurry (or "multi" in general) is such a broad theme to be put in a single category, and searches are difficult (e.g: "four arms" also matches "took me four hours but the arms aren't right") I've come with the idea of standard keywords for artworks including multifurry characters:

Base keywords:
multifurry : basic keyword. just tells the char is multifurry
hextaur: tells the character is a hextaur (or octotaur, decataur, etc...)
feral: tells the character is a feral multifur

Quantification:

_arms : number of arms
_legs : number of legs (not for ferals and taurs)
_hindlegs: number of hind legs (only ferals and hextaurs)
_forelegs: number of fore legs (only ferals and hextaurs)
_heads : number of heads
_tails : number of tails
_fingers: number of fingers (including thumb) on the hand with the biggest ammount of fingers
_penis: number of penises
_vaginas: number of vaginas
_breasts: number of breasts
_torsos: number os torsos (only split torsos, stacked torsos doesn't count)
_eyes : number of eyes on the head with the biggest ammount of eyes
_mouths : number of mouths on the head with the biggest ammount of mouths
_ears : number of ears on the head with the biggest ammount of ears

also for wildcard purposes, you can also add an extra tag with "multi" instead of a number.

For example, let's have a character who is a taur with four hind legs, two forelegs and two heads, one head has a single eye and the other head has 4.
The arms and forelegs must be ommited because it's the standard ammount. The eye count should be accounted because one head has 4 and of course, so does the head count.
That makes:
multifurry hextaur multihindlegs 4hindlegs multiheads 2heads multieyes 4eyes

I'm leaving this up for suggestions