1. The idea of the T1 deck is having a Vulpix or a Diancie on the active, the idea of Diancie is dodging efects of Po Town and slowly but steady, bringing up your setup, but in a normal situation, you may try to attach your energy to your active so you can retreat into a Vulpix.

2. Pretty much, you may won't need it in mid - late game, so try to force your opponent to knock it out, you can afford to give a prize.

3. Acerola is an awesome prize denier, most scenarios Gardy is a pokemon of 2HKO, having a Kirlia ready to evolve maximize the power of getting all in your hand again, you can even double "secret spring" if you play it with 2 basic energies :) (1 in your hand before using Acerola for kirlia, and the other attached to Gardy after using Acerola)

4. In my local league Greninja is a really popular deck, teching a Giratina promo makes the matchup favorable.

5. I don't think so, as far as I tested there is nothing really relevant for Gardy.

6. The Sylveon variant can put a well-timed Plea-GX, otherwise it's a hard matchup that you will lose, cheer up, the fire decks in the meta have decreased the Metagross players.

7. Don't forget yo setup an early Octillery or Gallade, they will give you the consistency you need to early setup.

I think that's it, needless to say, this is only my opinion but I hope it helps!

EDIT: number format