New to the club!!! All information will be appreciated!!!

[BIGSCOTTY70]

Well, after a very long time as a Chevy/Mopar domestic guy, I caught the bug (to put it lightly) after driving my first 350 then 370 and buying my first import, the new love of my life, my 04 G35 Coupe. So yes, I am a kindergartner learning how to color again! I've been working on cars and building them for 30 years, since I was 15 (yes, I'm old) lol
but have only done repair work on imports to date. So I'm here to be educated and absorb all of the knowledge that anyone is willing to share!!! After driving my buddies 370 Z Full NISMO loaded, I was hooked. I looked around for a while until I found a nice "starter" car. It's an 04 G35 coupe fully loaded with a couple of minor extras. As far as I can tell, only upgrades are a double din touch screen head unit with back up camera and an AEM cold air intake. The car overall is in great condition considering its almost 12 years old and has 191,000+ miles. But for only $5500, I just couldn't pass it up. Only thing I would change is that it's an AT instead of the 6MT. The car truly runs incredible considering the mileage but again, not sure of the complete history.
Anyway, in natural gearhead form, I'm looking at and reading everything I can get my hands on about the engine and best performance mods/combinations to get the most out of it. If I didn't say it before, let me say it now, I always try to squeeze every last drop of power and performance out of my toys!!!
So here's the first question before we go any further. Not knowing if the 191,000 is the true mileage on the engine or just the chassis, would it be fair to say that before I start adding power adders and tuning, should I bring it and have someone check to see if it had anything else done or go ahead and start a fresh build capable of as much power that I can throw at it? If I build one, it will be drop in, bolt up, and ready to tune and the current heartbeat will get a full build for, well, just in case.
Again, I'm a complete NEWB in this realm and want to know and hear as much as possible.
So, supercharged or turbo?
If I build, what compression should I go with to be able to get the most boost without blowing it out of the car???
Come on, help a new guy with all your wisdom!!!