Well as I said it wasn't a full on project because I didn't want to spend too much money and didn't want the car to be laden with further weight. My job basically consisted of three types of materials: lightweight cheap insulators from AliExpress which are essentially foam type material with tin foil type covering + heavy 3M sheets + 2-way tape.
The heavy 3M sheets are basically for roof type metal which is relatively thin and expansive, causing resonance. They add bit of weight to counter the resonance. Here's what I concluded after lots of research:
1) Wheel arches - the back side of the front arches have no insulation. Remove the fender shield from the back side (held to the body with screws) and placed lightweight material behind them (on to the metal body, not the back side of fender shields). Once you cover them up again, there isn't much chance of water and dust going into them. Rear wheel arches cause most sound so I removed the side bolsters from rear seats as well as trunk lining. Then arches body can be accessed. Here I applied the 3M sheets and the lightweight material on top of that.
2) Trunk - removed side as well as bottom lining. Bottom is strong metal so I only used the lightweight material as additional insulation. Sides are lighter metal so I applied combo of lightweight and 3M sheets.
3) The rubber into which the side windows roll up - this is a famous cause of wind noise in Accord. Its V-type shape, so I removed it and placed 2-way tape in between which makes it thicker and hence its outer side goes up hard against the window, eliminating small gaps.
4) Outside chrome strips rubber which goes against the 'foot' of windows - over time this rubber flexes especially at its ends and causes tiny gaps which let sound in through the doors and windows. Place another very useful insulation tape cut into small pieces inside it so that it goes up hard against the window, eliminating gaps.
What I DIDN'T DO - insulation of cabin floor, A/B/C pillars, roof, doors and the actual trunk diggi. The inner trunk lining is NOT an insulator, simply a cover. There are gaps in the molding where the number plate illumination lights reside - causing a lot of ambient noise to enter. But I didn't cover it as there are electrical connections. Can place lightweight material on the back side of the factory 'insulator' to make it thicker.
RESULTS - not earth shattering but I could definitely feel a clear difference compared to before.