This looked really fun so I thought I'd go ahead and post my in-game team I plan to use! :)
Decidueye: I wanted him from the start, Rowlet is one of the most unique starters I've seen in a while, and I really liked the fact that it's a mixed attacker (despite the fact that it's unpredictably slow). Spirit Shackle is gonna be a really cool Ghost STAB, and I'd imagine it gets access to Fly.
Vikavolt: This was the most difficult spot to fill for me. I wanted a nice and powerful Special Attacker, but something resistant or immune to Ground. Access to good stabs and it's insane Special Attack eventually led me to picking it.
Arcanine: I knew I wanted a Fire type to help against Steel types Decidueye and Nineties would struggle with, so I decided on Arcanine. With access to Intimidate it'll be a nifty defensive switchin, and it's decent array of coverage and priority ultimately convinced me.
Toxapex: I was torn between using this and Wishiwashi, but what sealed the deal for me was Baneful Bunker and Merciless. It's got amazing defenses on both sides, awesome defensive typing, and it's not dead weight thanks to being able to deal guaranteed critical hits against attackers with contact moves (despite its ironically low offenses). I have high hopes for this one.
Garchomp: I was lacking on speed, and I wanted a good powerful mega, so I chose my favorite pseudo legendary, Garchomp! Although Flygon now gets Dragon Dance, Garchomp's superior speed tier to start and mixed capabilities thanks to its mega sold it. It's also easier to train generally compared to Trapinch/Vibrava.
Ninetales: Ice Fairy is an awesome offensive type combo, and coupled with an amazing base 109 speed tier I finalized my team with Alolan Ninetales! It's able to help cover Garchomp's Dragon weaknesd, and be able to threaten most other Ground types that this team initially had trouble against.
Generally speaking this team can cover it's weaknesses exceptionally well on paper, and I'm pretty satisfied with it! I was originally thinking of other options over Arcanine and Vikavolt, such as Jolteon (extremely fast; increased my Ground weakness), Alolan Marowak (Dangerously powerful with the Thick Club; stacked a bit of a Dark weakness), and a few others, but this was the product I eventually put together. Feel free to leave a rate/suggestion, and thank you for reading!