I would recommend putting this in RMT, you will get better answers, and a complete analysis of your team. I'll give a few suggestions, but I'm not gonna do a full analysis.
First, trick room is very sketchy and can be played around pretty easily. I'm assuming this is in game, and not on PS! as you didn't give a tier, but even in game trick room is very sketchy. Trying to build sweepers out of tanks and walls sounds really nice, but in theory doesn't work well. They generally have a lack of good moves, or high enough attack/special attack or aren't the best typing. Even if you get trick room to work with a Pokemon, they can simply tank it out with someone like ferrothorn and then your "sweepers" are useless until you set up TR again.
That being said, you can still try and run trick room, but I wouldn't use this team. You have every single Pokemon relying on trick room, at least for the most part, and you only have one Pokemon to set up TR. You can try and set up TR with musharna, but I would have at least one normal sweeper in case TR fails.
To answer your initial questions about who your 6th Pokemon should be, I'm wondering who your considering, because you gave 4 Pokemon, and then gave 2 options for your 6th. Now, I'm not the best at math, but I'm pretty sure 4+1 doesn't equal 6 Pokemon :P
In all seriousness though, I would rather have conkeldurr, but replace rock slide with mach punch. Also I would add a eviolite rhydon, to help tank some hits.
I hope this helps you with your team, if you want more information, make a RMT out of this. If you have any questions or comments, please ask in comments!
On a side note, I'm back! Been awhile, but I'm coming back to the database because I have no life :P So hello everyone!