yep that's normal. throttle bodies, especially electronically controlled bodies work with a clearance gap for idle purposes. nothing to worry about at all, get yourself some brake cleaner or carb cleaner (basically the same thing) and give the inside of the throttle body a few scooshes and it'll clean up nice and good! feel free to start the engine with the air filter off and get your dad or someone to rev the engine and have a look at the throttle butterfly plate opening and closing, you'll see everything works as normal. cotton buds are a good idea if you want to be anal, certainly won't do any harm. brake cleaner on and then cotton bud the oil residue off. the oil comes from the PCV system, crankcase ventilation (this is the reason why some people install oil catch cans) lol
the residue you are seeing on your oil filler cap is also nothing to worry about, that's more than normal. it is water condensation from the crankcase ventilation system (oil breather) mixing with the oil, when the oil and engine is fully upto temperature, the water is evaporated out of the oil and all is good until you switch off your engine and then in the morning it's a repeat of that cycle. usually if you see a lot of this, it's an indication that you drive short journey usually anything less than 10-15 miles i'd say is a short journey! if you were to see absurd amounts of this, as in look down into the oil filler cap and all you see is this .... check the dip stick if it's on there too, then you're experiencing a cylinder head gasket leakage where coolant (water) is getting into the oil but that should be the least of your worries. that's for rover folks to stress about haha
I've never seen so much black dirt come off something before...