There really is no standard distance. It depends on the talent. Sometimes they want to eat the mic, sometimes not. Some really need to hold it. Some can't stand still. Some need to sit, though that's NOT recommended (yeah, what do I know? I'm just the engineer!!!). Depending upon what they want, I pull the appropriate mics out (hopefully) and test 'em out.

I put up my two favorite mics when I'm working with a new singer, and find the best fit - or the one I used last time if I've worked with them before. Then move the mic toward or away from the singer to get the best sound, which also depends, at least a little, on the room.

I ALWAYS use a pop filter. If for no other reason than to keep spit from hitting the mic.

Most threads and reviews I've read about which pop filter to use claim the metal ones are best. Maybe that's true for the sound. But I prefer to protect my gear too. So I use the "other" kinds - like womens' stocking material.

My favorite pop filter IS a lady's stocking (particularly if they are wearing 'em!), cut to size. Been using 'em since I saw it in the Let It Be "roof-top" videos backin the day. Works great, and doesn't distract...