I wouldn't bother checking until you see a problem, like difficulty shifting onto the biggest or smallest ring/sprocket, or the opposite: shifting off it. When this happens, it is not a "show stopper" problem. You can probably complete your ride, or even just pull over and make the adjustment right there.
There is usually a warning that the derailleur is going out of calibration. Before it becomes very difficult to shift to a gear, it first becomes slightly difficult and it progresses from there.
Regarding point 3, perhaps you're missing the plastic guard ring which goes between the casette/freehub and the spokes. Which is not to say that this is what prevents slippage, but it does prevent contact between chain and spoke.
By the way, one potential problem affecting the front derailleur, or at least some types, is that the entire assembly can rotate around the frame post to which it is clamped.
The front and rear derailleurs interact. Notice how it is easier to shift onto the leftmost sprocket when you're on the leftmost ring. So it cannot be ruled out that some rear difficulty is actually connected to a front problem.
One last piece of advice, and that is to install a rear derailleur protector, if you don't already have one. This part which installs on your wheel axle, held in place by the wheel lug nut. It extends a curved steel bar over the derailleur which guards it from being knocked around.