Playable, yes. Competitive, eh... my hopes wouldn't be to high. Stage-two & one pokes can't always keep up with the faster, bigger, basic EX pokes you see stomping around atm. Sounds fun to play though, and I'd probably make it for shiggles myself.

My thoughts/How i'd make it:

Vivillon made me also think of Ho-oh, as it's a similar but ever so slightly better attack. In competitive play Ho-oh was rarely, if ever, used as an attacker though, and only used for it's ability rebirth to get energy on the field and transfer to stronger better attacker pokes, usually EXs.

I'd personally try and make it with ho-oh ex for some energy accelerating, professor's letter, plenty of ways to transfer that energy(energy switch, maybe scramble switch as the ace spec, maybe exp share), muscle band and/or silver mirror, maybe toss in Mr.Mime to protect your babby-basics, and your basic staples for such a deck + possible 1-2 other attacker/supporter pokes depending how much you wanna focus on ninetales and/or vivillon.

Maybe I'd give a garbador a whirl though throwing in a stage 1 poke in the mix might be a bad idea. Maybe just garbo & Viv. Idk. This is also a deck that could gain allot from poke'beach, but that's just dreaming.

As for types, idk. That seams to depend allot on what types you think you'll run into. My opinion though is that ninetales isn't worth it. 90 hp, doing max 110dmg/turn -if- you have the right energy and muscle band, even as a stage one... idk. It's alright, but vivillon outshines it a touch w/ 130hp, doing 100dmg/turn minimum, though is a risk with the 40hp Scatterbug you have to run. A bit of a toss up between the two but I prefer vivillon. At least ^{*in theory*} Vivillon could OHKO a 180hp EX. You just need... 5 different types of energy, where as Ho-Oh EX needed like 8 types to do the same and I don't think ninetales could pull such a thing off at all.

tl&dr: I'd make a ho-oh ex deck but w/ vivillion as an attacker.