Here's what I'd suggest.
This post will be a little long.
You're going to need at least one more external drive.
I'm going to assume that you'd like to "migrate" your current home directory "right over" to the new one, correct?
I would try a "finder copy" of the home directory to the spare hard drive.
Note: I would actually copy the entire "Users" folder over, because I think that's the folder SA will "look for" trying to locate your home folder.
When the new iMac comes, do this:
Before you even turn it on, connect the home directory copy drive.
Boot the new iMac for the first time, go through the initial setup procedures.
When the setup assistant asks if you want to migrate stuff from another Mac or drive, choose to do this and "aim" SA at the connected drive.
You will need to check/uncheck the options in Setup Assistant so that it migrates ONLY your account(s) and settings.
You DO NOT want it to copy applications.
Now, let SA do its thing.
When done, you should have the home folder (your account) migrated, and your settings as well.
I suggest you log into the migrated account and "check around", to see if things (so far) look as you want them to. Of course, your apps won't "be there" yet.
NOW it's time to disconnect the first external drive, and connect the external SSD.
This next step could be important:
a. Once the SSD mounts (icon only), click ONE time on it to select it.
b. Type command-i (eye) to bring up the get info box
c. At the bottom of the box is "sharing and permissions"
d. Click the lock icon and enter your password
e. Put a check in "ignore ownership on this volume" and close the get info box.
This will avoid any permissions issues.
Once that's mounted on the desktop, launch Migration Assistant.
Again, you will have to check/uncheck through the options MA offers you.
This time, set it up to copy only Applications and data (if there's any data to be copied).
Once MA is set up, once more let it do its thing.
When done, all the relevant applications and data should now be in the NEW iMac's applications folder.
Take a good look around.
Try out each of your migrated apps.
Are you "where you want to be" ??
