How did you decide to go about it?
I pretty much went opposite ways: for Dragons I went whole-hog into the "fuck it, let's just cast Ur-Dragon" Timmy route (Urza's Incubator, Semblance Anvil, Gilded Lotus, even playing around with the Amonkhet Pyramid though I'll probably cut it because it's turned out to be too slow to assist in casting, hilariously enough) and Haste enablers (Temur Ascendancy, Karthus, etc.) to get those big meaty swings in. Basically cut all the cheap dragons (they aren't actually "cheaper" than anything else since they have double mana symbols anyway). Replaced a lot of the existing dragons with big-butt legends and mythics.
Conversely, for Vampires I actually loaded up on a lot of cheap value-pires like Shadow Alley Denizen, Stromkirk Noble, Falkenrath Executioner, etc. and a few more lords like Vampire Nocturnis and Lord of Lineage. And I filled out the lifegain->steal combos with Exquisite Blood and a Cliffhaven Vampire just to have alternate wincons. I'm trying to run it with way less ramp/fixing than I normally would for EDH, though, and I think I might actually have to cut some cheaper bloodsuckers for more rocks.
I'm still trying to figure out what I want to do with Cats, and I've already resigned myself to just tearing Wizards apart to make Kess Instants and Sorceries Tribal at this point.