These are not simple "here's the right answer" sort of questions. This is more like a process of learning......a bit of a journey, if you will.
I suggest that you start by using the "Search" function on this forum and doing some reading.
Paultergeist speakth the truth.
Seems everybody wants something different when modding the grom. Lots of parts out there to make it into any configuration that your wallet desires.
I will add that an exhaust + intake (chimera for example) + controller, you will not see (feel) any appreciable gains. The next step after those is where you will see gains. Yes an increase in displacement.
You need to educate yourself on the how's & why's of Grom modification. Someones advice may, or may not , be just what you are looking for. No need to buy twice from bad advice. Been there done that.
Good luck with your build!