You don't necessarily have to install Reflect onto the new NUC given that you'll be blowing away its current contents with the image of the old system that you'll be restoring onto it anyway. That's important to understand. Reflect will not "merge" your applications and registry from your old PC's image into the existing Windows environment on the new NUC. Everything on the NUC will be wiped out and replaced by everything from your old PC. Sorry if that was obvious to you, but it hasn't been to everyone.
Anyway, instead of installing Reflect onto the new NUC beforehand, try creating Rescue Media from your old system and using it to boot your NUC. If the Rescue Media you created from your old PC can see all of the necessary hardware on the NUC (e.g. the internal disk), then you should indeed be able to simply restore an image from your old PC onto the NUC's disk. If not, then you can either manually add drivers to that Rescue Media or install Reflect on the new NUC to build Rescue Media on that system.
But when you get working Rescue Media, if the NUC has more storage than the old PC, you should specify custom partition sizing during the restore rather than counting on expanding partitions afterward -- especially if the Windows partition is NOT the last partition on the disk. That mechanism is shown in Steps 4 and 5 of this article
. The article is for cloning a disk, but it works the same way for an image restore except the option says "Restored Partition Properties" instead of "Cloned Partitions Properties".
And then yes, after performing the image restore, you'll want to run ReDeploy. And after that you MIGHT need to run Fix Boot Problems. If Windows boots on the NUC at that point, you may still need to install some additional drivers, in which case do that just as you normally would.
At that point yes your applications, registry, etc. will all be transferred over -- because your entire old PC's disk will be migrated to the NUC's disk. If you're restoring a Windows 10 Pro image onto a new NUC that also has a Windows 10 Pro license, your Windows activation should be fine. It's possible that other applications might have problems, though. It depends on how their software licensing mechanisms work. Some of them might have problems when they notice they're now running on completely different hardware. There's nothing Reflect can do about that, so you'll just have to address that on a case by case basis with the vendors of those applications if needed.