For those interested:

http://tamrielvault.com/videos/16283/2324/the-first-horseman-of-the-apocalypse-pestilence

I've uploaded a video showcase of what the build looks like.

Thanks Vargr, really glad you enjoyed it!

[blockquote][b][url=/profile/Demoquin]Demoquin[/url] said:[/b]

How much disease damage is the hissing dragon perk doing?

[/blockquote]

According to the changelog of Ordinator: as of version 4.10, Hissing Dragon does 5 disease damage/sec and 8 poison damage/sec. I'm pretty sure this stacks.

There are actually some things I need to add/edit in this build. Discovered a few mods that are perfect for it. 

[blockquote][b][url=/profile/Demoquin]Demoquin[/url] said:[/b]

I was instead thinking of using a dagger and taking bite marks for the bleed damage.

[/blockquote]

That's what I do too actually! the more DoT attacks the better.

[blockquote][b][url=/profile/Demoquin]Demoquin[/url] said:[/b]

Does the corpse gas perk with rat king? So if one of the rats dies, the perk will kick in and spread poison about?

[/blockquote]

You're talking about the Conjuration tree right?

Personally I'd go for the perk A Plague Upon Thee (If a reanimated undead is destroyed within 20 seconds, the attacker is stricken with a Daedric disease that deals 40 damage per second for 20 seconds. Those who have this perk are immune.)

BUT to answer your question: fairly certain it doesn't. AFAIK the perk only affects REANIMATED undead, i.e raising corpses.

Well I'm fairly sure it doesn't affect Rat King sadly.

But if you wanted to experiment with a disease necromancer playthrough that'd be interesting too! Haven't tried that