Others will answer your 1st 2 questions better than I--some of the "Sticky" posts in this forum can help you too, as can the user's manual--but in my experience heavy Limewire activity can slow down your puter. 'Course, it depends on how powerful your puter is, the speed of your connection, your Limewire Options settings, etc., to name just a few factors.

Note that quitting Limewire doesn't cancel your in-progress uploads unless you have selected "Shutdown Immediately" in your Options, or you disconnect from the internet, or you turn off your puter.

As for your kind concern for the suffering of others when you shut down, don't worry, it happens *all the time*!. It's OK, you gotta do what you gotta do. And yes, when you shut down, downloads are continued from other hosts, if there are any who happen to be online and sharing the same file at the same time. Also, if a download does happen to quit due to a host going offline, it can be picked up again later where it left off, from any host who is sharing the same file.