Hi, first off welcome to the wonderful world of VGC. It's very different to singles in many different ways. The main ways I find it different are as follows (this mostly also applies to other doubles formats too, like DOU):
- Protect is a staple. It allows you to improve your board position, abuse obvious double targets, stall turns of tailwind/trick room/weather/terrains/fake out etc.
- Intimidate is incredible, should probably try to include in almost every team.
- Spread moves are a thing.
- Games are much faster, for a fairly obvious reason when you consider 4 Pokemon move per turn as opposed to 2, and only 4 Pokemon are brought by each player.
- Because of the above, particularly defensive/stally playstyles as well as setup are heavily deterred.
- A whole host of moves which are useless in singles are viable and strong in doubles, for example redirection moves like Follow Me and Rage Powder, Fake Out (occasionally used in singles, but much more in doubles), Wide Guard (Protects your team from spread moves for the turn), Quick Guard (Protects your team from priority for the turn), Feint (Breaks the target's Protect for the turn), Trick Room (again occasionally used in singles but much more common and viable in doubles), other speed control options like Icy Wind, Tailwind, Thunder Wave etc.
- EVs tend to be a lot more specific than the common 252, 252 spreads you will see in singles and tend to be tailor made for specific teams, mostly because of how fast paced the metagame is, so living certain attacks is crucial to a win condition. The metagame also often revolves around 10 or so Pokemon that you are very likely to see (in the current format, examples would be the Tapus (except Fini), Oranguru, Celesteela and Alolan Marowak, but there are plenty more), so living certain hits from these and ensuring you KO these with particular attacks is important. That being said, 252,252 spreads often are just the most efficient spreads, especially on focus sash users for example where bulk isn't the number 1 priority.
That's all I can think of right now, but I'm certain there are other things that I'm forgetting and you will learn when you start playing.
As for what you mention, Ninetails right now is an interestinng niche pick. Aurora veil is definitely a great move, though I'm not sure pairing it with Pheromosa is the best idea. Pheromosa is incredibly squishy, screens or no screens, meaning it really relies heavily on its focus sash. Considering hail will break your focus sash, I just don't think Pheromosa and Ninetails are a great pair. Regarding entry hazards and Toxic, hazards are straight up non-viable in VGC and Toxic is generally considered a poor option. This is again due to the short nature of battles and the fact that 'walls' don't really exist. Matches don't last long enough for the benefit that you gain from setting up hazards and getting chip damage on switches outweighing the opportunity cost of clicking the move and not having a better move in its place in the moveset.
As for Toxapex, it's an interesting choice but it's very passive. Other than wide guard, it doesn't seem to provide that much support. It kind of just seems to sit there. Sure Scald burns are annoying (wish it got a nerf), but you can usually play around them and other than that you can kind of just ignore it and double target its partner.
Now, you talk about breeding your team and then practising with it. You really don't want to do that. It's very unlikely that the first team that you ever decide to make will be perfect, or even good. Especially considering you don't have any prior knowledge of VGC fundamentals or the current metagame (I briefly covered that I guess but that's definitely not enough information to make a strong team). You really should familiarise yourself with the format first (either through playing around on showdown, watching youtubers who know what they're doing, or both), make a team, test it on showdown, make any alterations and test again (repeat those last steps until you are comfortable with it) and then breed it and play with it ingame. Even if you have a general idea of what your team composition is going to be, there's nothing more infuriating than making a spread that requires a certain nature for it to be optimised and that isn't the nature of the Pokemon that you have bred ingame.
Now, this is the third time I've suggested these youtubers to people new to VGC, so forgive me for just copying and pasting what I have said previously :P
https://www.youtube.com/channel/UC9OZkS1Mhl5UvKSiPrYqsxg
https://www.youtube.com/user/CybertronProductions
https://www.youtube.com/user/TheKylecol3
Wolfey has been putting out great analyses for the new Pokemon, including sets with calcs explaining what the EVs are there to do (should help with creating spreads on your own) and potential partners.
Cybertron posts great daily battlespot lives with his full thought processes. He also recently created a great teambuilding guide for beginners I would highly recommend checking out.
And finally Kyle Cole posts some cool showdown lives as well as Pokemon analyses and recently made a 'Good VGC Cores' video which is a great starting place for teambuilding.
Sorry I haven't suggested a team for you to use. If you want to try out a team using ninetails, you can probably just take one of the teams that Kyle Cole uses and test that out on Showdown and maybe make some alterations if you feel comfortable doing that.
