With all respect I was kinda chuckling at you while reading this. I agree if the mods do not make sense to you, don't spend the money. You are 100% correct the stock ST is pretty sweet no upgrades needed at all to have a good time. But then the moding bug bites you. I really do not want to sound rude but you would not have came here if you did not want a discussion, so here are my honest thoughts.
I liked the symposer too at first, I thought for sure would never remove. LOTS of people have said that before on this forum. Trust me you will get sick of it. I dont have an exhaust (though I dream of having one), but after removing the symposer I will never put it back on. It is this simple. Do you like ricer zoom zoom noises, or real engine growl? Thing is our 4 cylinder is amazingly good at creating a fairly deep tone, it sounds great in its natural state, it just is not very loud without an exhaust. Do not get me started on that wonderful sound of your turbo spooling once you upgrade the intake, you definitely want to be able to hear that with the windows down, the symposer just gets in the way of that.
Then also I definitely understand the desire to stay away from tuning, I definitely do not disagree with anyone who is worried about warranty/reliability issues, I definitely had that frame of mind at one time too. But you research the reliability of tuners & the options seem pretty solid. So eventually you convince yourself you will just give it a try & go really easy on the car, only use it once in a while. You buy yourself a COBB Accessport as they are clearly the best option out there. At this point you are ****ing scared man, you dont want to ruin your brand new car. But you install the tune anyways because everyone keeps telling you it will be "fine" and really "awesome". So okay installation goes through just fine, you sigh relief, did it really work? You take the car out for a spin to find out. It does not take long at all, first take off & you come to the realization this car has so much more potential than the factory allowed it. The boost can jump to 3/4 on even the slightest attempts. The butt dyno tells you you are definitely going way too fast.
Next thing you know you are shopping for an intercooler. Installing motor mounts. Getting high end tires. Eventually you fall victim to the big turbo crowd. Its terrible **** man. You are probably good to stay away.
p.s. welcome to the forum. Let me re-iterate, no harm in staying stock, you still get mad respect here regardless because we are all in on the big secret: Focus ST's are freakin sweet.