2001 S4 In dire need of help...
 

Just bought a 2001 Audi S4 w/189,000 miles but in absolute beautiful condition other than drivers seat having duct tape on it,the dash info screen appearing scrambled and impossible to read, and what seemed to be calcium build up behind the engine on some hoses... This is my first Audi and sadly I only got to love it for about an hour then it happened at a rest stop... coolant leaked out everywhere. Replaced immediately with r/o water and got it to a mechanic 1 mile up the road, but not before the speedometer gives out on start up. He then got it up on a lift and diagnosed a coolant pin whole leak and revealed a huge oil mess bottom of the car, seemed to be mostly old an dry, but signs of a new or smaller leak still present?.!.The mechanic then gave me the okay to drive 300 miles home. Stop to gas up next where my finance says to have pumped premium but I'm still unconvinced to this day that's what gas was put in? We then continued on home, an hour later I notice what's seems to be a misfire but have to continue on. On the next day I get diagnostic codes po300 multiple misfire & po501 speed sensor, later day reveals pm1131 bad o2 sensor. bank 2 sensor 1 "is driver side correct?" All sensors were reading something to the tune of 435 and 575 which I believe is called limp mode.?? Changed plugs, mechanic claimed coil pack on drivers side middle is faulty and does appear to be burned on the boot, "I agree". I change plugs to autolite double platinum "having to set the gaps though the plugs were supposed to be preset", purchase 2 duralast ignition coils replacing the one bad, purchase speed sensor but no clue how to get to it and to change it. Also purchased Bosch universal o2 sensor which is not installed yet, and coolant is still undecided as the car is parked for maintenance. Sorry this is so long. To conclude, can someone give me some advice because the car is still running rough.
CURRENT CONDITION:
At idle it has a minimal shake? On take off the car is hugely limited in power and sounds of puttering to chugging are apparent. @25 to 2800 rpms it smooths the engine a but but still no power and turbos are clearly heard breathing at 3000 to 4500 rpms... Any ideas ... on my mind is Vag-com but not on my current budget this week..