I would go with the following minimum
120 archery
100 tactics (damage bonus at 100)
100 hiding
75 stealth (75 is minimum required not to fail in all mediable armor)
100-120 ninjitsu (ninjitsu gives better chance to animal form, as well as determining if poisoned shurriken hit/miss)
Optional stuff:
Anat, Healing, Spirit Speak (for res ganking), Resist
Equip wise you want
45 HCI, as much dci as you can get, all 70's, 40 lmc, 100 DI, enough mana for at least 2+ specials (you will probably qualify for 2nd mana discount), mana increase, MR2, HP increase...
best helm for you is either mace & shield or spirit of totem.
enhance your bows to 40 ssi. you will probably want balaned to chug potions. balance also allows you to throw ninja stars/fukiya darts without disarming the bow.
Statwise depending on items I would put 125 dex, 100 str, 30 int. you want either 150 or 180 stam, with a buffer zone so your swing speed doesn't drop. you can achieve this via dex items, potions, +stamina on armor. ie if you have 130 dex, +32 in stamina items for 162, you can chug a dex pot and be at 180+ stam...
tactics:
start out with dismount from heavy xbow
poison mount and them using shurriken/darts
use mortal if they heal, else use ai/moving shot
smokebomb shares skill timer with hiding, and you cant smokebomb if you've been mana-vamped and have 0 mana.
it is a challenging toon, since you wont have the offensive or defensive ability of other characters. not to mention being in right place/right time to land dismount, but not get piled on by all his friends. if you are field fighting and you dismount someone i would recommend smoke bomb, people are smart and know to pile on the stealther during a dismount