Wow, I'm even later to this, but I think you scored! Especially if it came with all those extras, the splash guard thingy included. This is I think a link to the user manual online, which might be helpful:
https://www.kitchenaid.com/content/dam/global/documents/201407/useandcareguide-w10388644-revd.pdf
As far as maintenance, I found instructions on replacing the grease in the motor, but it can be a little tricky to get the head unit back together, and when I asked a question of KA, they said they don't want us to do any motor maintenance ourselves. Things to look out for are any scraping of the beater/whisk against the bowl -- there's a screw in the hinge area that can help slightly raise the top part to avoid the friction - and if you use the mixer for a long time, like ten minutes of kneading dough, keep an eye our for any oil leaking from the head unit, which can happen if it overheats and the thick grease broke down over time.
There are a couple of YouTube videos on carefully cleaning your mixer.
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