Numbers and math are required for theoretical space travel, but not necessarily for practical space travel. Catching a ball requires solving differential equations, but children and animals are capable of performing this action with no problem.

Given that there is so much of physics that we have yet to understand (assuming what we think to be true is actually true), and given the infinite possibilities of what forms alien life could take, you can't make any assumptions about what sort of language they'd have. This was a point they briefly tried to make in the movie.

Another way to do 'practical space travel' without 'theoretical space travel' is with tools. Just because you can't develop it with your language doesn't mean you can't use a tool someone else developed, or even an animal that evolved with the capability.

I don't know if that is true. I agree with you, but the obvious counterpoint is that a lioness has cubs and raises them to be apex predators just like herself, all without a language. You don't need a language to do things, there are many stories of people living just fine lives without language. To get to the stars, I'll bet on your hypothesis, but I think given enough time, some alien somewhere may have done the same without a thought in it's 'head' at all.

Larry Niven's "stage trees" - basically, naturally evolved rockets for seeds - spring to mind, where the space travel is an instinctive, unconscious behaviour.

But I'd bet on the OPs hypothesis as well. At a guess, most space travelling species will have had to climb a similar developmental curve to our own - including agriculture (or whatever passes for it in their biosphere, unless they photosynthesize themselves), tool making, metal smelting, nuclear power, etc. etc.