You can download the Factory Service Manual for free here.
http://www.clubfrontier.org/forums/f23/frontier-service-manuals-available-download-46290/
You shouldn't need to change the plugs yet - factory service interval is 105,000 miles.
Go take a look in the DIY forum at the stickies - you'll find a lot of the info you're looking for like transmission fluid changes, rear differential, etc.
http://www.clubfrontier.org/forums/f23/frontier-service-manuals-available-download-46290/
You shouldn't need to change the plugs yet - factory service interval is 105,000 miles.
Go take a look in the DIY forum at the stickies - you'll find a lot of the info you're looking for like transmission fluid changes, rear differential, etc.