I don't really have many tips besides just brute force it lol. If you understand how mania works already from 4k, that's a good start, but learning and improving 7k is just a matter of playing it a lot. For me, I just played 1-2 stars for like a week or two until I could S or FC them consistently, then kept moving up the ladder of difficulty. The advice here is basically just stick to it even though it might be really difficult and unfun towards the beginning.