Please, for the love of god DO NOT PUT A SPOILER ON IT!
-It WILL NOT make you go faster, it's added weight
-You DO NOT NEED IT, a spoiler is to apply down force on the rear wheels for better traction and stability at high speeds, the keyword is rear wheels, and your civic is front wheel drive.
It looks better clean, go for a sleeper look
As for mods
-Bigger Turbo
-Bigger injectors
-Bigger Intercooler
-Build the engine with higher horsepower tolerant parts
-Strip interior, get rid of everything you dont need use light weight parts
-New clutch, flywheel
-Bigger rim size with wider tires
Honestly, if you want to have a race car, a civic wasn't the greatest choice, you can make it fast with enough money... but with the money you'd spend on all-of-the-above parts you would be better off buying a shell of something better like a 240sx, Mustang, Camaro, Supra, something meant to be fast, and building it from the ground up. Good Luck