Many thanks Gael. Moreover, thanks for the documentation on nilearn in general, as this had made these important analyses accessible.
Completely understand what you are getting at. As a didactic practice (prior to posting), I worked with a single subject (no issues), and then two subjects concatenated, (intermittent issues, cannot consistently replicate) and then got through the full sample once ('kernel died ... restarting'; but got through it). I have looked at memory usage during and it's high for each machine we've tried it on. So on the 18.8 GB of the full sample perhaps might be an memory issue, I'll work to push it to the server and check there where memory shouldn't be an issue.
I appreciate your thoughts, will keep you posted as things get resolved and we scale up (I'm hoping to apply these approaches to larger data sets). There is a far amount of assurance in more experienced feedback (even if the issue is not completely resolved), as we are working through these the analyses the first couple times.