If I had a Gym, I would be a Steel-type Gym Leader. My entire Black 2 team was Steel-type, I didn't use a starter at all, unless you count a Lucario as a starter. I would name my badge the Mercury Badge.
Though i'd prefer to be a mixed gym like Green is. Honestly I like battles for the fact that don't have a "theme". He was a hard leader/champion because of that, and that's why I liked him so much, his diversity.
I'd also like flying type with
Garydos[for some spice]
and Emolga or Charizard [also some spice]
Even though morty was already a ghost type gym leader, I don't mind becoming another one. I would name the gym badge as spirit badge.
My roster would be as follows:
Chandelure (My favorite ghost type pokemon)
Sableye (I think its secondary dark type helps a lot with ghost and dark type opponents)
Froslass (its secondary Ice type can easily handle bug type pokemons)
Gengar (This, along with Chandelure, are great special attackers)
Jellicent (It's a pretty bulky ghost pokemon, great special defense)
Drifblim (Also another bulk ghost pokemon, its secondary flying pokemon works very well against bug types)
a Pokemon - of the existing pokemon, I'd go with either a smeargle 'cause they could paint anything they see, or a lucario,
Gym Leader - I don't really have a favourite type, but would probably be a grass gym, with sceptile, meganium, venusaur, cherrim, whimsicott and the final evolution of chespin, 'cause I feel like it
Champion/Elite 4 Member - for the elite four I'd be a fighting elite four with blaziken, toxicroak, gallade, scrafty, and lucario (if there were a rematch option I would just add a sixth gen fighting when they come out)
A Ranger - my partner pokemon would be emolga, a good scout and overall cute pokemon
A Trainer - I would raise pokemon that were approximately human sized or man-made (easier to train) and I would train them relatively easily, with a mix of battling and taming.
If you had any Pokemon Ability - I'd probably go with cloud nine, 'cause hey who wants to be dragged down by weather
If you had any Pokemon, which one would you have? - Altaria or Flygon because they're my favourite dragons and look like good company
And pretty much anything else.: the very best like no one ever was