So I was thinking about this, when a coin is new you can only mine using cpu.
Not necessarily. Unless the coin's algorithm deliberately makes it difficult to use a GPU, people using GPU rigs will have a lot advantage and you will have to compete with them.
During that time you can mine a lot coins per day with only your CPU.
Only if you are really really fast, and only if no one is mining. Hard to achieve these days, you would have to have some kind of insider information.
I mean theorytically CPU mining is way more profitable then GPU mining, if you can get in at the right time. Could there be guys who only by mine by cpu(and making profit) even if they could easily afford gpu rigs
This is not true in general. Again, it depends on the algorithm.