Before I answer how slow should a Trick Room team be, there are a few couple I need to cover: What kind of Trick Room teams there are, and that different formats have different Trick Room abusers (Pokemon who benefit from the effects of Trick Room), which vary "how slow" a Trick Room user should be.
1. Types of Trick Room Teams
how many Pokemon should be able to benefit from the effects of Trick Room?
This depends on what kind of Trick Room you are using. There are two types of Trick Room teams: Full Trick Room and Semi-Trick Room.
Full Trick Room: Full Trick Room team is exactly what is sounds like, a team that has just Trick Room setters and abusers. On a full Trick Room team, you would have two or three Trick Room setters, and the rest of the team would be Pokemon who abuse Trick Room. If you think of Full Trick Room teams as just a slower team, Full TR is basically Hyper Offense, but with lower speed stats.
Semi Trick Room: A Semi Trick Room team is a type of Trick Room team where it has Trick Room setters and abusers but isn't a full Trick Room team. Semi TR teams have no more than 1-2 setters, 2 abusers, and the rest of the team is Pokemon that are used outside Trick Room.
Should there be a fast member on the team in case I'm unable to set up a Trick Room?
If you are using Semi Trick Room, then yes, you should have fast Pokemon for outside of Trick Room. If you use Full Trick Room however, you don't need a fast Pokemon.
2. Different Formats Have Different Trick Room Abusers
The format was never mentioned, and the format you play in factors into "how slow" a Trick Room team should be. For example, Gen O OU and UU have Trick Room abusers such as Melmetal (OU), Alolan Marowak, Conkeldurr, Azumarill (UU), and Crawdaunt. NU has TR abusers like Glastrier, Marowak, Stakataka, and Alolan Exeggutor. PU has Pokemon such as Glastrier, Aggron, and Wishiwashi for TR abusers. ZU has Pokemon such as Trevenant, Gourgeist (Large) and Exeggutor. VGC has Pokemon such as Calyrex-Ice and Palkia for TR abusers. Different abusers have different base speeds, meaning that "how slow" a Trick Room team will be different in each format.
If by "how slow" a Trick Room team should be, you meant how many Pokemon should be able to use Trick Room, read the section of the types of Trick Room. If you meant how slow should the Trick Room abusers be, there isn't a set standard on what how slow a Trick Room abuser should be. Most Trick Room abusers usually have a base speed around 30-70, but there are a few execptions of Pokemon with higher speeds abusing Trick Room. There are also even slower Pokemon who abuse Trick Room such as Stakataka, Mega Camerupt, and Escavalier.
As for the Pokemon with higher speeds who abuse TR, these cases are from the VGC format. One example is Kyogre, a Pokemon with a base speed of 90. Kyogre's Series 12 VGC analysis says that Kyogre's base 90 speed works with Trick Room should it use a bulky set. Another example is Palkia, who has a base speed of 100. There's no VGC22 analysis for Palkia currently, but its VGC21 analysis mentioned that it worked well on bulky Trick Room teams. These examples show how the format you play varies into how slow a Trick Room team should be.
TL;DR How many Trick Room abusers you should have depends on if you run a Full Trick Room team or Semi Trick Room team. Full Trick Room teams have 2-3 setters with the rest being offensive TR abusers. Semi Trick Room teams should have 1-2 Trick Room setters, 2 TR abusers, and the rest of the team should be fast Pokemon for use outside of Trick Room. How slow the abusers should be depends on what format you play. Most TR abusers are usually around a base speed of 30-70, with a few slower Pokemon like Escavalier and Stakataka. There are some Pokemon with a base speed around 90-100 who abuse TR such as Kyogre and Palkia when used in the VGC format. Do note, that the speed range isn't a set standard, as there isn't one when it comes to how slow a Trick Room abuser should be.
