I'm making a little 2D game in C++ using the SDL framework, but it's one thing I've thought a lot about while I have worked with the development of the game... is it bad to use vectors too often, and should I rather use arrays than vectors?
Personally I almost always use vectors instead of arrays, since vectors increase automatically in size.
It depends on your needs and the use case. There is benefits to using std::array over std::vector but generally that is only when you don't need a dynamic size (You know that the number of elements will stay the same for the lifetime of the object).
Now will it make to much of a difference if you do use std::vector all the time? No, most likely it will have no impact on the performance of you application since I assume it is small in size. Though when you get to AAA size games it is definitely something to be taken into consideration because of performance aspects and memory aspects.