-I like SMG's for ninja classes, especially the UMP, feel free to change this to your likes, you can use the Assault Rifles too! , but if you want to be stealthy you should be close to the enemy, so be careful of what you choose!
-For this, your best bet is a machine pistol, there powerful and got good ranges, you either want PP2000 or M93 Raffica both silenced. Or if u wanna rush a bit u can go for g18/silenced
-I would pick Marathon. Then Cold-Blooded and Ninja. You need to make sure that every perk listed is Pro. Their Pro abilities are VERY important. If u dont like my option u can try going other combos that keep u stealth.
-Claymore is recommended for this class, but it on high traffic areas and you can get loads of kills, and you can use stuns for slowing down the enemy or smoke for cover. I prefer stun, because if i enter a building and know theres some1 there its just to stun em.