Unfortunately, FoGP is now banned. Luckily, Sky Field would probably be the best stadium for the deck even if Forest weren't banned.I made a decklist for this a while ago, here's a link to the thread: http://www.pokebeach.com/forums/threads/future-zoroark-gx-vespiquen.140926/
Mega Ray and Yveltal are two of the most popular decks in Expanded, and without Jolteon you cannot OHKO Mega Ray with Zoroark. It would be nice to fit in some of the other Eeveelutions, but the list is tight on space and Jolteon is definitely the most important.I like your list, but I think Vaporeon would be better than Jolteon since Volcanion is so good in Expanded (although you can K.O Volc without it it makes it that much easier). I think you should drop a Sky Field for a fourth Sycamore and Colress for a second Egg. Also, I think Choice Band or Muscle Band would be good additions but I can't see where to fit them.
Zoroaek is stage one and I think night march is way better as it can deal twice as much damage.I don't think it would be the best fit with Night March. The strength of Night March is that it does tons of damage really fast. Zoroark is a stage 1 that you can't accelerate the evolution of. Plus, it's not really necessary for the late-game–Marshadow was added to the Night March for that.
In Vespiquen, Zoroark can be used as an early-game attacker, so you can get Pokémon into the discard while attacking with a Zoroark or two before finishing the game with Vespiquen doing 200+ damage.
Another card that could be paired with Zoroark using the same philosophy of attacking with Zoroark while your other attacker sets up would be Trashalanche Garbodor. Late-game, Garbodor could do tons of damage, especially in Expanded, where decks play lots of items to set up really fast. Running two types of energy might be kind of clunky, though, and Vespiquen/Garb didn't see much success either.
Vespiquen can do even more damage than Night March, it just needs more time to set up, which Zoroark gives it. Plus, Night March has to be really consistent and streamlined. Adding a Stage 1 does the opposite: it makes it more clunky.Zoroaek is stage one and I think night march is way better as it can deal twice as much damage.