Try Brand. He has good base damage, a stun, and good poke. Plus it's very dangerous to engage on him because his ult is great in 2v2 situations. Plus his passive will scale as the game goes on without needing ap.
Not terribly bad. He has amazing sustain with his W and his Q does enough damage for him to be a threat if they target him. He can basically build tanky and still do good damage. The only bad thing about him as a support is that if you get ganked, there is very little you can do to protect your carry. You can knock them back with your E if you have good positioning or use your ult, but both of those have long cooldowns.
Viable? Yes, just hope your carry has flash or you might be sacrificing yourself fairly often.
Yeah, it's been noted that Hecarim's passive and size allow him to deny by standing on top of minions, so be sure to try that if you play him again. Also a question: is Nid support considered viable? Because she's perfectly suited to it.