Here's a thread that starts to answer some of your questions.
http://www.classiczcars.com/forums/s...highlight=280z
As for a forum with step by step instructions that doesn't really exist but you usually will find multiple threads on many types of common repairs by using the search function.
As for manuals I'm biased towards the Haynes manual but, depending on what year Z you end up with, the factory service manual may be online or could be gotten off of EBay.
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