Ej205 is safe to ~330-350 range
ej255/7 is safe to the 400-450 range depending on some factors.
A cai when having a proper pro tune is a fine mod for subbies. They just don't pick up much and in the case of short rams they sometimes lose power. I've made 300-330awhp on the stock airbox.
The ebay tmic works, I've got a IAT sensor in the IC and on freeway pulls and my temps stay flat . and i previouslly made ~370whp using this same top mount.
The most overlooked part is the turbo inlet. so many people get hta68s and are sad when they can't make the power they want.
What is your budget?
08 wrxs can be had cheap and you can swap a 09 turbo onto them for ~600ish