Karen doesn't need the money. In the pilot Grace says that working makes Karen feel grounded. Karen typically didn't cash the paychecks that Grace gave her - but she admits at one point that she enjoys getting away from her husband and her stepchildren during the day.

No, never. In a flash back in episode 3.8 "Lows in the Mid-Eighties" a year after Jack and Will first met, Jack confesses he's in love with him. But Will immediately lets him down easy and Jack (obviously lying) says he was just "testing him." Later in episode 5.24 "24" Will and Jack awake naked in bed together after a night of drinking and since they have no memory of what happened, it appears they've slept together and the season ends with a cliffhanger. In the first episode of the following season, Karen reveals information via surveillance cameras that nothing happened between them.

We never find out exactly. Throughout the beginning of the series, it was comically implied that Karen could be incredibly old. In one episode she accidentally lets it slip that she lived through the Great Depression, but due to the presumably millions of dollars she's spent on plastic surgery she looks much younger. But in the middle of the series, Karen's mother, Lois, comes into the picture. Lois works as a barmaid and can't afford excessive plastic surgery. Lois appears to be in her late sixties.

No, it's entirely forced. Refer to the Pilot episode to hear her real voice. Throughout seasons one and two she slowly transitioned to the more comedic, squeaky voice which wasn't realized during the development of the series.

Not really. In the premier of season three his hand and feet are briefly seen; in 4.9 "Movable Feast" he's silhouette behind glass; and in episode 8.4 "Steams Like Old Times" he has a conversation with Jack and Karen in a sauna, but his face hidden by the steam and his voice is drowned out by the hissing, sauna mechanics. Overall, throughout the series, his face and voice are never directly revealed in any way. TV director James Burrows' trademark for which he is known is having a reoccurring guest character who is never seen. Audiences responded well to this because a character whose appearance, thoughts, actions, and desires being entirely revealed through second hand information from the main characters made for good comedy in itself. In Burrows' previous show "Cheers" Norm's wife Vera is never seen, and in his following spin-off "Frasier" Niles' wife Merris is never seen. Ironically Stan is the one character universally liked by everyone else.

Supposedly, they were going to have Marlon Brando play Stan but he died before they could get it together.