The mixed sweeper are Nidoking, Zapdos 3 attacks, Tyranitar, Gengar? Are there others?
That's kinda a question on how you define sweeper. The mixed attackers in this gen are mostly used to break walls, not to actually "sweep". When building a team in gsc you are usually not narrowing down the roles of your pokemon to do one thing. Let's take Zapdos for example, if you boom on raikou and lax beforehand your zapdos is sweeping, if you use it to switch into exeggutor to absorb a sleep powder and swing the tempo into your direction it's a pivot. If you use it to stall out a nidoking it's a wall. If you critpara their raikou so you can win is it a wallbreaker? Like Jorgen said, everything is a wall, everything has defensive capabilities that you will usually need to make use of, that's why there are no real dedicated sweepers in this tier (zard and others that are named are boarderline exceptions).
There are many viable mixed attackers that can potentially sweep on top of the ones you named. Mixlax, Machamp (fireblast); Exeggutor, Cloyster (explosion); Clefable, Charizard, etc.
Growth pass is a good strategy? Who is better to implement it?
It's viable. Vaporeon, Jolteon and Espeon are the usual passers, everything that has special attacks and wants them to be stronger is a potential reciever. I see Zapdos being the main reciever usually, the possibilities here are very broad though.
But the cleaner in this generation there are none?
Like I mentioned above, teambuilding isn't as narrow that you can say "this is the pokemon that i kill everything with in the end". There aren't many typical cleaners, it's mostly about breaking the opponents team. You can call drumlax a cleaner, you can call it a wallbreaker, you can call it utility and you can call it a wall, it usually ends up doing most of those roles in every battle. This just applies to almost everything in gsc.
I do a lot of questions because I want to play something more strategic than traditional Boom team in this generation.
What do you define as "more strategic"? Is wearing the opponents key mons down with spikes, status, etc more strategic than killing them with explosion? I have really no idea what you mean by that, there are many offensive strategies you can try, paralysis + belly drum, spikes + mixed attackers, explosion, baton pass, spikes + toxic + offensive pressure, setup mons with proper support, ... Just toy around and find the strategies that fit your playstyle the most.