yeah the tools are a must if you don't want to scratch up the case.
and you might be able to piece together all that, the case, jack and battery for cheaper....I don't know. sometimes you can, sometimes you cant.
also, unless the battery is old and not holding charge like it used to....I wouldn't change it. Aftermarket batteries tend to not work as well as oem batteries.
I know. It's just that all the classified with a back case also include a free battery. And I think for <20 bucks total it's not really that bad.
Then again some more searching revealed you can get opening tools + jack for about $3-4 shipped.
Edit: Nevermind, thats for the 6th gen nano. Wasn't paying attention.
I found this:
http://www.ebay.com/itm/Headphone-Audio-Jack-for-iPod-Classic-6-6th-80GB-Free-7-Tools-US-/380683916340?pt=US_Replacement_Parts_Tools&hash=item58a2879434
It does not include a hold switch, but I can just use my own, right? And it seems all the 6/7th gen iPods share the same audio jack, but I'll check this just to be absolutely sure.