Hello and Welcome!! I also discovered discovered the series through the anime, and I definitely agree with you about it having a unique charm and quickly becoming attached to the characters.
So after looking up all the songs, which became your favorites? 
Thanks. I started rewatching some episodes and I'm loving it!

I love just about every Im@s song out there and how there's a ton of variety. But there's a few that hold a special place in my heart.
Top 3 765 Pro songsi - My first ever fave from the anime. They used it for the ED montage for ep 13, right after their debut concert and also as an instrumental version for several emotional scenes throughout the show. So whenever I listen to this song, I feel a rush of nostalgia and a strong case of "the feels" because it always reminds me of their journey to being top idols. Hoping it eventually becomes DLC for OFA, or they give Hibiki a master version.

Nijiiro Miracle - THIS. These are the kinds of songs that I love about Im@s. Songs that fill you with joy, full of hope, that inspire you to do your best in life.
Music♪ - I don't know how to describe it, but this song just hits me hard every time.
Top 3 Image/Personal songsSora - Fell in love with this song the first time i heard it. I'm kinda hoping they release an all-star version of this, sorta like what they did in their concert last year, where all the idols sang the last chorus together.
Shiny Smile - Being a Hibiki fan, I sure you saw this coming!

I used to listen to this song before bed.(im@s2 Hibiki solo) Any other fans shed tears of joy when they found out they were finally giving her a master version in the latest master artist album? I know I did.
Suteki Happiness - So I was watching all the EX songs one day...I thought Makoto's was really cool, Iori WOULD sing something like that <3, Yayoi being adorable as always, as expected Chihaya never ceases to amaze, Island themed song for Hibiki? Heck yes!...I was pleased with the songs they gave each idol, however I was still hesistant to listen to Haruka's. I thought hers was gonna be so generic, since when it comes to songs I always thought she got the short end of the stick. Was about to hand over the medal to Pon De Beach, but then I noticed her vid got more views than all of the others so I was like hmmm? Decided to watch it.

I was so mesmerized. I liked Haruka as a character but singing wise I felt like she was never given a song to truly shine. This was exactly what I was looking for; a song that fully brings out her personality. Whew, damn. My eyes were sweating happiness like there was no tomorrow. Go Haruka!
I feel like there's more that deserves special mention like Uzuki's super warm S(mile)ing!, and Anna's Happy Darling, but I don't wanna drag this post on any longer than it already is.
Hmmm...Spoiler tags for images don't seem to work.
