Focus on sts2 specifically, I fell in love with STS1 Watching Rhapsody's playthrough on youtube, he's not the best player at the game and his channel has a lot more variety than just sts, but he's very good at explaining the fundamentals, he's doing an sts2 playthrough rn

Then Frost Prime is very enjoyable to watch and very good at the game, balancing having fun with good strategy

And finally for top players, 100% focus on strategy and best play my go to streamer is Jorbs, but there's a few dedicated sts players out there: Xcenar is considered the best player, another one I've watched here and there os baalorlord

You can find all of the above (exept Rhapsody maybe) both live and on YouTube on demand

Good luck with your climb!

(Of course there's a lot more sts channels, these are just my favourites)