For 300 hp, I'd say get a decent boost gauge, a drjonez manual boost controller, and turn the boost up a bit. Gut your cat, and make sure to get a BIC downpipe to go with your catback and intake. I'd also recommend putting ARP head studs in making sure they're torqued down properly to reduce the risk of a BHG. Then, you should be pushing the 300 mark. Gurus, did I miss anything?
As for 400 hp, that's gonna cost more. There are a dozen different things you can do from swapping on a bigger turbo, to adding nitrous, to a front facing intake with a higher flowing head... each option will have its own benefits and drawbacks, and each one will require a different combination of the others to work properly. I'd say once you reach this point, you should sit down and completely plan your engine before moving forward. One of the biggest mistakes we can make is to move ahead on a build without thinking and in turn waste time and money, and do a shitty job.
I hope this helped!