What if I will combine triangles and squares together in one object, can that make my object more broken in some ways when rendering? Do I have to make my object only with triangles or only with squares?
No, it is perfectly fine to use both triangles and squares in an object. For example, the object below has squares and triangles, and it works just fine.
As discussed in the comments below, there are many reasons why you might prefer to work with squares when modeling instead of triangles, but you can definitely use both if you wish.