Damn sorry this happened! I ordered the v3 front splitter for my Si and I chose local pickup it did take them like 3 weeks to make it or get it read. Luckily I live 15 minutes away from them so it worked out perfectly.
What is your budget and how loud are you trying to be? There is the Greddy Supreme sb exhaust, Greddy DDR exhaust, AWE touring or track, Thermal, Indivia etc...
Here is a clip of some exhausts for the 10th gen and how they sound.
I also have a 2020 si. Sedan in black. I am also around 4400 miles and the highest mpg i've gotten is 28mpg right now im getting about 27.8 with a ktuner and prl cobra intake with street maf. I usually drive street.