Upgrade to GD coils (sticky) and don't worry about the coil pack.
You can swap out the entire intake manifold, turbo, airbox, etc. for the EJ20K one if you wish. Re-use the EJ20G engine harness.
The only issue you will have to deal with is the TPS. The EJ20G TPS has 4 pins and incorperates an idle switch. The EJ20K has 3 pins and no idle switch. The throttlebodies cannot be swapped directly because the throttle cable is on opposite sides.
I have seen attempts to use the EJ20G throttlebody on an EJ20K intake manifold. You use a spacer to gain some clearance and mount it upside down to get the throttle cable on the correct side. Then you have to deal with minor hose and pipe issues. FWIW, I haven't seen anything more than attempts, nothing running yet. But close.
If it were mine, I wouldn't worry about it. There is argument that the EJ20G intake manifold is superior. WRC cars use a VERY close looking style. The 90 degree inlet on the turbo is considered the restricting factor, but going rotated turbo mount solves that problem nicely if your targetting those HP levels.