Playing a ROM of FireRed, my first pokemon game ever, what’s a good place to grind? and also should i change out any pokemon for the e4

Basically the title, i’m thinking about switching out my Machamp for a level 30 Gengar and grind him up. If you’re wondering how I have trade evolutions, I used a save editor only for pokemon i already had that couldn’t be evolved.

I already tried the E4, got dogwalked now I need to grind. Any places?