iMac Pro and Migration Assistant

I'm wondering if anyone has has success using Migration Assistant in setting up their iMac Pro. If so, how did you do it? (Connection to the other mac over ethernet, connection to a Time Machine backup drive via USB or Thunderbolt, etc.?) I've been trying to set up this new mac this weekend and I'm now wiping the drive and reinstalling the OS for the second time, and wondering what I should try different next time.

Full details (in part from an earlier post):

First attempt: I tried to use Migration Assistant during setup from our old Mac Pro (10.10.5) to the iMac Pro. The Mac Pro has a USB 3 card but when I connected them with the Belkin USB 3 to Thunderbolt cable with the Mac Pro in target disk mode, the iMac Pro didn't see it. I then booted up the old Mac Pro with them on the same network (ethernet, not wifi). Then the new iMac Pro could see the Mac Pro, but the Mac Pro could not see the iMac Pro and the migration could not proceed. After some time on the phone with Apple Support I tried hitting the back button to go back to the beginning of setup and then both macs cold see each other and the migration proceeded. (If there's a next time I'll start Migration Assistant on the old mac first.) I should note I did not copy over applications, I'll reinstall those.

Next problem was that once the migration was complete, on the new iMac Pro any time I touched a file the OS would decide it was "damaged and can't be opened. You should move it to the trash." After reading up on the problem, talking to support again, and trying a few things including reinstalling the OS, I erased the iMac Pro's drive and did a clean install of the OS. Then I updated the old Mac Pro to Mac OS 10.13.3 and got an updated Time Machine backup. (The theory is that Migration Assistant has some as of yet unresolved bug when transferring files from 10.10 to 10.13, and upgrading the old Mac Pro should eliminate that problem.)

Second attempt this morning: rather than connect to the Mac Pro, I put the Mac Pro's Time Machine backup drive in a Thunderbolt 3 enclosure and tried to use that in setup. I was concerned about whether this would work since the Time Machine backup was backing up both a system drive and a data drive, and I only wanted the system drive copied over (the data drive will move into the enclosure) but it looked like it was going to work. This time I excluded Applications and Settings, copying over only user data and "other files." Unfortunately after upgrading iTunes it almost immediately said "Migration unexpectedly quit. Please try again later." But it had created accounts anyway such that when I tried Migration Assistant again it wanted to create new accounts instead of copying over the old accounts (the "replace accounts" option was grayed out).

Third attempt: I'm now wiping the iMac Pro's hard drive and reinstalling the OS (again) and wondering what I should try next. Connect to the old Mac Pro over ethernet again? Connect the Time Machine drive via USB 3 instead of Thunderbolt? If you have suggestions or success stories let me know.