Yeah, that was my one issue, too. I love them as a duo and knew they would become one, but I felt like it was missing another episode or two centered around them.
I was like "oh huh we're doing this now?"

Ahhh thank you so much for reading my essay and sharing your thoughts!!! 💜

Episode 8 was the debut of their group song, TRIAD FORCE! Here's our lyrics and styling for what was in the episode.

files.catbox.moe/vbkjak.mp4
#プリオケ

Also randomly getting new coords is also just a thing that happens in Pretty Series. There's usually no particular rhyme or reason to it unless the coord itself is important to the plot. (Such as the Seventh Coord in Rainbow Live.)
Thank you for reading and sharing your thoughts/opinions btw!!

Also as far as the tournament/grand prix/whatever goes, it's very much par for the course with Pretty Series to wait a while before introducing major events.
(PriPara's second season, for example, while still mentioning the new system, took eighteen episodes to actually get to the Grand Prix.)