One the flaws of Tapu Koko + A-Raichu lead is the fact that A-Marowak (which is really popular on BS right now) completely shuts down their Electric-type attacks and threatens both of them with Bonemerang (a 2 hits move that bypasses your Focus Sash too).
This shouldn't stop you from using this combo, however you would need to play as smart as possible against A-Marowak, the random Scarf Garchomp you may encounter and against other Tapus too.
The first thing you can do is to add a Gyarados whose Intimidate and Water/Flying-type is a great switch-in against an opposing A-Marowak and Garchomp. However it doesn't give you a safe switch against a strong LO Psychic from Tapu Lele in Psychic Terrain and you still take a lot of damage from a -1 Wood Hammer from Tapu Bulu, which means you should definetely add a Steel type in your team. The one who would fit perfectly in this core would be Celesteela: bulky Steel/Flying-type, it can switch into Psychic, Ground and Grass moves without problems and it has access to Wide Guard and Heavy Slam to threaten the opposing Tapus.
This is just an input, you can find alternatives too but the idea of having safe switches to keep the momentum in your favor is not bad at all.
This shouldn't stop you from using this combo, however you would need to play as smart as possible against A-Marowak, the random Scarf Garchomp you may encounter and against other Tapus too.
The first thing you can do is to add a Gyarados whose Intimidate and Water/Flying-type is a great switch-in against an opposing A-Marowak and Garchomp. However it doesn't give you a safe switch against a strong LO Psychic from Tapu Lele in Psychic Terrain and you still take a lot of damage from a -1 Wood Hammer from Tapu Bulu, which means you should definetely add a Steel type in your team. The one who would fit perfectly in this core would be Celesteela: bulky Steel/Flying-type, it can switch into Psychic, Ground and Grass moves without problems and it has access to Wide Guard and Heavy Slam to threaten the opposing Tapus.
This is just an input, you can find alternatives too but the idea of having safe switches to keep the momentum in your favor is not bad at all.
