Passat (B5) :: 2002 - V6 Tip FWD - Missing Coolant After Timing Belt Changed

My car recently had its timing belt changed, it's got about 83k miles. up until then there had been some oil loss, but there was some leaking found around the valve covers so the gaskets were done. my mechanic did a full tb change, including the water pump. he said that the coolant was pretty cloudy when he changed it too.

When I got the car back, the coolant filled the tank to about half. it was running and warmed up (had just been driven about an hour) at the time. this was a couple weeks ago. i haven't driven the car since then as its my wife's ride. today, after i got to work (hour on the highway) and turned the car off, i checked the coolant level. it was at the min line.

Now of course, my first thought is "oh crap, am i really gonna have to do a head gasket now?" But I'm wondering what else might be going on, particularly after a TB change. Also, the car has been running kind of like crap as of late. I changed out the spark plugs, which were clearly OEM, and that worked immensely, but after a ride on the highway for an hour it's a bit rough getting off the highway. Dunno if it's related - my mechanic also thinks i need to replace my wires too, so perhaps it's just that.

So far it doesn't look like my oil is being consumed, though i need to pay more careful attention to that as the days go on. i do get a burning coolant (i think. could be oil, but I'm pretty sure it's coolant) smell from the vents when i warm start the car and turn on the heat. it goes away in about a minute or so. when i first got the car back, my mechanic said it was due to the coolant he spilled all over the engine, but after two weeks i wonder if it isn't something else. i suppose it could be, but the car's been driven about 400 miles since and i would think it would be gone by now. maybe i need to clean the engine to be sure? So, questions:

1) Is it possible that there was some air in the system, and that the air worked its way out, causing the overall level to go down?
2) Are there any likely areas of the TB job that could cause this? i don't recall it ever consuming coolant before, and at this rate, i certainly would have, i should think - we had the car for a year before this.
3) The car had a bit of sludging in it - guess is that it never had anything but dino oil before. So I changed it out with some 502 rated oil and my mechanic advised me to drive it hard every so often and then change it out before my normal interval. today i put it into manual mode and got my rpms up around 6000. could the high rpms have led to consumption in some way?

At this point i'd like to collect as much info as i can about this before making any decisions about how to proceed.