There are a million different ways/opinions on how to do this. My 2 cents is that you should set up your new iMac from scratch with fresh user account, install all your software, etc.
Then copy over your the data from your old user folders into their respective new user folders (e.g. Documents, Movies, Photos, Music, etc.). You can either do this over a network connection by sharing folders, or generally faster and more straight forward to use an intermediate external drive.
I recommend this way because you've accumulated 8 years of cruft scattered throughout the system (or whenever you last did a clean install), and IMHO it's a good idea just to start with a clean slate. And personally I trust myself to make sure everything (and only what) I want migrates over more than I trust migration assistant. It really doesn't take very long these days with so much data in the cloud that's just a matter of signing in (e.g. mail, dropbox, evernote, etc.)
But there's nothing "wrong" about migration assistant or any number of other ways that might be suggested.