If I'm not mistaken a Stage 1/2 flash does not "require" any other mods. However I have started putting together a "wish list" for future motor upgrades and these certainly would increase the performance of a stage 1/2 flash....
PRL High Volume Intake System
PRL Street Downpipe & Front Pipe Combo Upgrade
PRL Intercooler Upgrade
PRL Plug 'N Play Flex Fuel Kit
PTP Turbo Blanket
And if you really want to go full race (Type R) mode -
Honda Civic Type R Turbo
If you aren't familiar w/some of these parts take a look into our
How To And DIYs board in the threads posted by @
tommypenguin.
If you were to add some/all these mods I would definitely suggest getting the car professionally tuned as the flashes provided by Hondata/KT will be for a stock (other than the tuner) car.