Intro to CS can vary a lot - it can be an incredibly hard class at some places and sort of easy at others. Is the class made for non-CS majors or is it the first in the major track sequence?
Discrete and Linear Algebra will be relatively easy, especially for a math major.
Calculus II can be hard for some, easier for others. It’s not an impossible class, but it isn’t a full cakewalk.
I haven’t taken number theory, but I’ve heard it’s a hard but interesting class.
Overall it’s a lot, but it should be doable. It does strike me as odd that you’re bulking up on all major classes so early - it could be just a bit easier to add in a class that isn’t math. There’s also the risk that all the classes start to blur together and cause problems that way. 4 math classes worth of homework could build up quick too. Unless there’s a specific reason you’re doing this, switching a math class for another subject could be nice.