I have a 2011 sedan Sti limited. I'm currently running: cobb cold air intake with box, cobb turbo back exhaust, and v3 access port with 91 oct boost map ext.
First off, do you live out west where 93 octane isn't readily available?
If 93 octane is readily available, I'd definitely recommend it and start using the 93 octane off the shelf map.
Turning up boost is possible if you were to install a manual boost controller, but doing this without tuning is a surefire way to damage your engine. The best way would be to get a protune on a dyno (though [MENTION=9]HolyCrapItsFast[/MENTION] does do e-tunes). Most tuners use some sort of Open Source tuning, but you can go on Cobb's website and see if there is a tuner nearby you that uses Cobb Accessport compatible tuning software.
http://www.cobbtuning.com/dealers You can still run an Open Source tune, but it will only be saved on the ECU. With an AP compatible tune, you can save it on your Accessport and so forth. To get the most out of your protune, you should install an upgraded fuel pump and probably injectors as well (though you might get away with putting that off until later). NGK Iridium one-step colder (part #: NGK LFR7AIX) plugs is a good idea.
If you want your turbo to last, 20 psi might be a little too much. I'd shoot for 18-19 instead. If you want more boost that that, you'll have to consider a turbo upgrade.
At that point, things can get more complicated.
As far as an intercooler goes...do yourself a favor and refrain from buying a front mount unless you upgrade the turbo. Even then, the general rule of thumb is, a big top mount can support up to a GT30 turbo. Unless you are installing a turbo around this size or larger, a front mount is going to contribute to lag and reduced throttle response. If you must upgrade the intercooler, try to find the largest top mount possible that can be installed without modifying anything under the hood (such as upper coolant reservoir). This will give you the best combination of charge cooling and throttle response, while allowing you a bit of room to grow.
I've gotta get back to work now, but let me know if you have any other questions.