Reliable? It's doable, especially at modest power levels. The best thing you can do is read read read. Read and take notes on what mods you think you want to do, compare your findings to what others with similar mods have gone through. This is what I've done, and with good success. My power mods are limited to:
-Cooleeze Turbo-back Downpipe
-HKS Sport Exhaust, 75mm piping (resonator removed)
-AEM Dryflow Filter (too many horror stories about oiled filters messing up afms)
-Blitz Super Sound BOV on upper Hardpipe section
-Speed-Source Lower Hardpipe
So, my car's just an average BPU, but I love my car--I love the responsiveness, the sound, and the feel of the car. I'd love more power, but I'm afraid it's going to take a steady stream of money to upgrade it more and keep it in the tip-top shape I'm used to it being in--I'm pushing 155k miles, and I'd rather do some freshening up on the bottom end before I go big--at the very least, a new oil pump and new rings are in order.
I have spent a good bit of money on the car, much more than the above mod list would suggest. Much of it was spent on interior pieces, suspension, tires, brakes, and paint repair/care, but a portion of it was spent on performance-supporting upgrades. You may be able to get away with doing a list of performance upgrades similar to mine up above without these parts and be completely ok, but I wanted the peace of mind of knowing I had new, reliable parts in place.
These upgrades you should consider:
-New vacuum, coolant, pcv lines--basically any rubber under the hood that feels hard could be replaced. I think the only original rubber hoses under the hood on mine are the 2 hoses from the ISC to the accordian hose, and some of the rubber on the intercooler piping. Makes a big difference and you KNOW that you don't have to worry about a pinhole coolant leak or a vacuum leak throwing things off.
-Water Temperature gauge and maybe a Boost gauge--The stock gauges really don't tell you much, except when there's a serious problem. You may not need a boost gauge really until you start upping the boost--you may see a few psi increase with the dp/exhaust and intake upgrades, but the stock gauge should be fine for these mods. However, the water temp gauge upgrade I would strongly recommend. Since I've had my GReddy gauge, I now know that my stock temp gauge reads normal from about 80*C all the way up past 105*C! It's nice to know if your temps fluctuate at all, especially if you're troubleshooting an issue.
-Cooling System Checkup
-Radiator--This may be over the top, but if you are unsure of the past maintenance of your cooling system, these are (relatively) cheap insurance items. If the top of your radiator looks old and dry--check it for hairline cracks. These cracks can cause the cooling system to lose pressure, lose coolant and overheat.
-Fan clutch--Check the fan clutch for fluid leakage, and see if you can spin the fan with the engine at operating temp BUT TURNED OFF--if you can spin it, it may not provide enough airflow to cool the engine.
-Water Pump--In regards to the water pump, depending on the types of coolant (or lack thereof) that has been run in the system, and the frequency of changes, it may be time for a new one. I have good reason to believe my water pump had something to do with my first HG failure, which occured shortly after a flush and coolant change from green to red. The fins of the pump were corroded badly, and couldn't provide enough coolant circulation.
Anyways, hope this helps some, I'm sure other, more experienced members will provide much more concise info--but I felt I'd try and help state what's worked for me.
