Questions about Nebulites

The boxes give out rank D and C nebulites, and very rarely a B.
While you can fuse them, it's unlikely you'll get anything good out of a few boxes.
And if you have the meso to buy plenty of boxes, just buy the nebulites themselves in FM.

I know a few people who make a decent living merching off opening boxes and selling the nebs. I've never tried it myself so I can't say for sure, but at 2m a box, buying 100 boxes lets you see ~200 nebs, and a single 2% stat B neb makes you your money back. It's why I haven't sold my last few stacks of boxes.