If you want to work or do internships with other organizations while in NUPOC that is entirely fine and actually encouraged if it is Engineering/Technical in nature, just so long as doing so is not a detriment to your studies.
(Disclaimer: There are no guarantees of what future market returns might be, and I'm not telling you that you're going to get rich because of this program -- this is a sidebar public service announcement from me personally to everyone reading this that you should start investing early because the benefits are much greater for saving now vs. starting 15-20 years down the line. I've simplified purposely here to make a point. Even at a lower return, say 7%, that initial investment would be over half a million at age 68. That same initial investment at age 40 would only be ~$80k. Do yourself a favor and go do some independent research.)