yup, sounds like classic air-oil separator (AOS) failure.
what you need to do is look inside the throttle body and/or J-tube for more than just a misting of oil. my TB looked like this: (more below...)
that liquid is black gold/texas tea compliments of the AOS not doing its job.
as far as your oil level is concerned, the dash oil gauge only shows (approx) the top 1 liter of oil. when the gauge shows no 'bars', you are down 1 liter/quart. there are still ~8 liters left. the oil gauge level will change periodically and will certainly not be accurate right after you shut the car off. oil in the engine passages needs time to get back to the oil pan to be measured. when you pulled over and shut the car off, there was still plenty of oil in the passages. after the car sat for a while and most of the oil had made its way back to the pan, you then saw a full display on your oil gauge.
additionally, over time oil becomes contaminated with gas and water (normal by-products of combustion). if you take short trips where the engine does not get up to operating temp, more gas/water gets in the oil and gets measured along with the oil. when you drive at operating temp and at high revs, this will remove some gas/water and you may notice a substantial drop on your dash oil gauge as a result - although you have not lost any 'oil' at all. this is also normal, and will allow you to get a more accurate oil reading. the best time to check oil is first thing in the morning after the car has been sitting all night and the oil has had plenty of time to return to be measured.
in a perfect world, you want to reach engine operating temperature every time you drive the car (10-20 minutes of 'normal' driving). and you don't ever want to 'warm up' the car by letting it idle in the driveway. what i do is start the car, wait 15-20 seconds for the oil to get where it needs to go, and then drive gently, not going over 4K RPMs until the engine is up to temp (5-10 minutes after the coolant temp reaches 180). once the engine/oil/transmission/suspension is warmed up, feel free to get that tach all the way to redline if you want. (also known as an 'Italian tune-up') ;) these practices will keep gas/water in your oil to a minimum and allow all the car's metal engine/transmission parts to expand uniformly and slowly. your engine will thank you for it. :)
to answer your questions:
1. the computer (OBD-II system) is giving off more codes because your problem is getting worse. (i.e. the AOS is feeding enough oil into the cylinders that it is causing misfires). you should start fixing things at the AOS. this is the beginning of AOS failure as you are only having misfires in Cylinder 4, the first cylinder on the driver's side (right behind your back). if you don't change the AOS, the oil will eventually make its way to all cylinders. it is very good that you caught this early.
2. i would not clean the MAF yet. wait until you've changed the AOS and you get a CEL. you want to isolate the problem and if you clean the MAF AND change the AOS, which one was the problem part? (although it is quite obvious it is the AOS). plus, your MAF may be fine and if it ain't broke... ;)
3. can you drive the car as long as the CEL is not flashing? yes, except when you suspect AOS failure. the AOS could feed enough oil into your engine that the engine fails (catastrophically). DON'T drive it.
4. the AOS' part number is on the top side of the AOS. then look on the Pelican Parts Part Lookup Catalog http://www.pelicanparts.com/PartsLookup/HT...USA_KATALOG.htm in the Engine section under Crankcase Bleeding and you will see that the latest AOS for your car is 996-107-023-04-M100. it really doesn't matter what the old part number is because it has failed regardless of whether it is the latest model or the original. my guess is that it is the original. AOSs usually go bad around 60-80K miles.
5. after changing out the AOS, change the spark plugs. after you remove the old plugs and before you put the new plugs in, give the engine a few quick 1-second cranks by turning the key. this will blow out any remaining oil in the cylinder(s). the car obviously will not start as there are no plugs in. ;) after that, put the new plugs in and make sure all the coil pack connectors are firmly connected to their ignition wires (they SNAP in). here's a pic of the connection. the rubber boot is pulled back so you can see where it snaps together.
don't forget to also buy a new J-tube (part # 5 in the diagram below). the 'accordion tube' or 'bellows' (part # 10) comes with the AOS (part # 1). all the necessary fasteners/clips are included. you will re-use the mounting screws from your old AOS.
if you are not due for an oil change, you don't *need* to change the oil. if you *want* to change the oil, that's up to you, but it's not necessary. check the oil level via the dipstick and just top it up if it needs it.
i have found that www.SunsetImports.com and www.SuncoastPorsche.com have the best prices, but in this case, Pelican's don't look too bad either. figure $120-130 for both the AOS and J-tube + shipping. it is a rather simple DIY replacement; however, access is the hard part. here's a link to the DIY with pics. http://mike.focke.googlepages.com/airoilseparatorreplacement
and here's a diagram:
good luck!