Just briefly looking at the pokemon you're using, there really is no need to make this an uber team. You should bump it down to OU. Now here's a case-by-case overview of your team:
Overall, this is probably your most problematic set. The thing that sticks out the most here is flamethrower, and your decision to make him a mixed sweeper. Get rid of flamethrower (you already have STAB and fire coverage through flare blitz) and replace it with Iron Tail. Next, the EVs are a bit of a mess. With only 56+ on speed, even with the scarf, you're going to be outsped by Ash Greninja (which is quite common in OU) or anything else with >130 base speed. Run it with a Jolly nature, and 252 attack and speed. With this, you'll ouspeed everything that isn't also scarfed and because of that, you won't need the HP investment you're currently running.
This set's pretty good, but I have to call out a few things. First, I would run Outrage instead of Dragon Claw. Next, I would replace either Poison Jab or Iron Head with Stone Edge for rock coverage, and because both of the aforementioned attacks serve the same purpose as a fairy counter (if you take my advice and give Arcanine Iron Tail, I would suggest replacing Iron Head, keeping p-Jab). Finally, I would put full 252 EV investment into attack.
If I had to suggest anything, replace the item with Leftovers, if there's no item clause (which there isn't in Smogon's OU tier). If item clause is a problem, then Maranga Berry is fine.
I noticed that you haven't given the EVs or nature for this one. If this is because you are unsure, then I would suggest either 252 HP / 252 Def / 4 SpA or 52 HP / 252 Def / 4 SpA / 200 SpD, with a Bold Nature in either case. Otherwise, looks good.
I would change the EVs to favor the defensive stats, so that stockpile will boost them even more. Here's the spread I would use: 104 Atk / 152 Def / 252 SpD.
I feel obliged to point out that your team has a prominent ground weakness, in particular, I could see this team having trouble with Landorus. Additionally, outside of maybe Magnezone (who's really more of a tank), you don't really seem to have a good special sweeper. Keldeo could easily fill both of these spots as a special sweeper and Lando-counter:
EVs: 4 Def / 252 SpA / 252 Spe
IVs: 0 Atk
- Secret Sword
- Hidden Power [Ice]
- Calm Mind / Hydro Pump / Focus Blast
I had some trouble deciding on an item, but I think your best bet would be to give it a z-crystal, replacing Gyarados' with a Gyaradosite and upgrading it to Mega-Gyarados.
If you like this Keldeo set, I think it would be best to swap it in exchange for Gastrodon.
Those are my suggestions; hope they help! Your title suggests that this is your first competitive team, and if that's the case, good job. Good luck and happy battling!