Welcome Bruno! My first mod was exhaust cut-outs and is still probably my favorite mod.
I much prefer the cut-outs rather than putting catbacks on. If you are not buying the Camaro new you may want to consider a professional tune, it made a big difference in my SS. Strut brace isn't just a pretty mod but it actually makes a difference in the cars handling.
As Pluto mentioned a CAI is a "must buy". I wanted something different than what everyone else had so I bought a G5CR CAI and have had zero problems and haven't thrown any engine codes. I haven't seen another Camaro with a G5CR. Dash ABL and footwell lighting are great mods. I'm not a fan of the catch can and haven't put one in my car. I know a couple of people that put them in their car and they get hardly nothing going into them so I just don't think it's worth the money. Maybe they are worth it and I'm missing out?
I have done so many mods on my SS it's hard to recall all of them.
Russ