Best way to migrate using Time Machine backup

Question

My wife has an '08 iMac. I think it originally had Leopard. Along the way I updated it to Snow Leopard and then Mountain Lion. It also has an external USB hdd and we've used Time Machine to backup to it since we've had it.
We just picked up a new iMac with Mavericks. It's still in the box. I'm under the impression that I can just power up the new one, start Migration Assistant, plug in the external drive, and it will copy all her stuff over from the latest TM backup.
Is that right? Is it that simple? Are there any known issues or gotchas?
I've searched and seen issues from people that turned out to be caused by anti-virus software. I'm assuming that out of the box that won't be an issue.
I also saw a reference to a TM "clone" backup. I don't know exactly what this is. Do I need one, or any other special TM backup, or should the default TM backup work?
I've also seen references to Setup Assistant being used to migrate data to a new iMac. Would I be better off using this or Migration Asst?
I saw a link that I thought would answer that, "Transferring data with Setup Assistant - Migration Assistant FAQ", but that just takes me to the top-level support page. I also saw a link to setup instructions from Pondini, but that requires me to log into iCloud, which my account can't do. I think my wife's can, so I'll try hers and check it in the morning.
Anything else I should know? Anything else I should tell you before you answer that?
Also, any idea how long this should take to migrate? Her internal drive shows 400G used.
Thanks for any advice.
-cb

Answer 1

Thanks very much for the response.
mende1 wrote:
As you are using an USB external drive and you probably want to transfer a lot of files (you say that the old internal drive shows 400 GB of used storage), it may take several hours. I do not recommend you to transfer everything or you may experience performance issues (if you had problems in the old iMac)
Can you elaborate on this? Do you mean we shouldn't restore apps, or something more fine-grained? We're mainly interested in her data (docs, music, photos, etc.).
Yes, the old one gives occassional WSODs, which was part of the motivation for the upgrade. I'm unclear on whether it's due to one or two specific apps. She always seems to have lots of apps open.
I have a follow-up question. I saw an Apple migration page that said after migration, if you don't plan to keep using the old iMac, then deauthorize it from iTMS and turn off "find my Mac" and sign out of iCloud. We are thinking of giving the old one to our 3-year old. Should I do the deauthorize, etc. or just create a new account for her, or does it not even matter?
Thank again.
-cb