First team ever

I'm a new player and I decided to create an OU team with a rather standard Skarmory + Chansey core for my first team in order to get some basic experience.
I'm currently 3-0 with it, which is always nice, but the question i'm asking is: Is the team actually any good, and what can be improved?

Skarmory @ Leftovers (Physical wall and lesser hazard setter)
Ability: Keen Eye
EVs: 252 HP / 252 Def / 4 SpA
Impish Nature
- Roost
- Spikes
- Brave Bird
- Whirlwind

Chansey @ Eviolite (Special wall)
Ability: Natural Cure
EVs: 4 HP / 252 Def / 252 SpD
Bold Nature
- Toxic
- Soft-Boiled
- Seismic Toss
- Wish

Gengar @ Life Orb (Sweeper)
Ability: Levitate
Timid Nature
- Shadow Ball
- Sludge Wave
- Focus Blast
- Taunt

Garchomp @ Lum Berry (Lead, hazard setter and setup sweeper)
Ability: Rough Skin
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Dragon Claw
- Stealth Rock
- Swords Dance

Azumarill @ Sitrus Berry (Bulky to take hits for Chomp and Belly Drum sweeper)
Ability: Huge Power
EVs: 92 HP / 252 Atk / 164 Spe
Adamant Nature
- Belly Drum
- Play Rough
- Aqua Jet
- Knock Off

Raikou @ Choice Specs (Sweeper no. 2 and also a lead)
Ability: Pressure
EVs: 32 HP / 252 SpA / 224 Spe
Timid Nature
- Hidden Power [Ice]
- Thunderbolt
- Volt Switch
- Shadow Ball

Thanks in advance.

Sturdy is the preferred ability on Skarmory, as it ensures Skarmory does something from full health. Keen Eye is absolutely useless in comparison.

This team appears to be offensive, and Chansey tends to be dead weight on these kinds of teams, due to its passiveness. It functions best in stall teams, where the Skarmory + Chansey core can truly function at max effectiveness. A better replacement for Chansey is Mega Altaria. It has better offensive presence in Pixilate-boosted attacks and still has good special bulk. Mega Altaria can cover for Skarmory's Electric and Fire weaknesses:
-Return/Hyper Voice
-Earthquake/Flamethrower/Roar/Perish Song
-Heal Bell
-Roost
Nature: Impish/Bold/Relaxed
EVs: 248 HP/104 Def/156 SDef
Item: Altarianite

Platdude offered the suggestion of Mega Altaria which isn't a bad idea since your team currently lacks a mega evolution. While you don't need one, you will be at a disadvantage from other teams since mega Pokemon are so powerful and generally are the core of a team.

Also just a personal preference but I feel like BD Azumarill is really bad and the choice band set is better, but again that is just my opinion. You may also want to look for something that can clear hazards as LO Gengar doesn't want to be taking any unnecessary damage as well as Raikou who will be coming in an out pretty often. Chip damage does add up more than you think. Also clearing hazards helps ensure your Skarmory's sturdy isn't broken upon switching in. Just a thought though!