The "black oil" is normal, it's due to soot collecting in the oil. It turns black very quickly after an oil change, so don't let that worry you. It's also not unusual for these to leak. See if the shop can identify the sources and give you an idea what it would take to fix the leaks. I wouldn't worry about driving it in the mean time. If it's leaking keep an eye on the oil level, you want it to be be about halfway between the two marks on the dipstick after it's been sitting for a while. Wipe of the dipstick, then check the level. Also, take a look at your coolant (antifreeze) level in the tank, it should be about half full.

Your oil pressure should be around 1-2 bars when it's idling hot and pinned at 3 bars whenever you're above about 1000-1500 rpm. Your temperature should be in the 80-90C range (ideally) but they sometimes get up around 100C under load. If it approaches 120C, you want to stop and let it cool off.

There aren't any specific sounds to listen for, unless you hear something that's clearly unusual. These engines are pretty indestructible as long as you don't run out of oil of overheat them severely.