Can stock sequential turbos on fd support about 350-380whp with the following mods?
1. intake
2. full 3"+ exhaust
3. radiator
4. boost controller
5. power fc
6. water injection, necessary?

 

350-380 is pretty much maxing out the stock turbos.

You will also need fuel system mods, an intercooler, and it would good to add an ignition amp. You might not reach the 380 mark without at least a streetport.

I would definitely include the water injection because the stockers create a whole lotta heat plus the engine will be running hard. The water injection will make a big reliability improvement.