What is proper etiquette when hosting a dinner party with seated service and multiple courses?

Unless the wait becomes really tiresome (and that becomes clear by the fidgeting of the guests who are waiting for the next course) then each course is served to all guests at the same time. If the conversation at the table is lively, most people will not notice that there are laggers; but should the wait become difficult, simply announce the next course and have it served. The laggers will wither relinquish their plates, or ask that they be left. In that case, honor the guest's request. You'll sometimes find, particularly at a multiple course meal, that some will not eat all they are served. It is not necessarily a signal that the food is unsatisfactory, but may be a sign that portions are very generous.

You have to use your own judgment on this one. You can't set a timer for eight minutes and then yank the plates away when the timer goes off. On the other hand, a guest who is dawdling or playing in his/her food, showing no interest in actually eating it should not be allowed to hold up the show.

Use a reasonable amount of time between courses. If a particular guest is not finished and not willing to give up his bowl/plate, he can push it to one side and accept the next course. You may have done this on occasion in a restaurant.

if the meal is not progressing with your schedule, do what i do: walk to the window, peer out, and announce, "Oh, they're towing cars." that will get them chewing.