Well that is good news to hear both ends, eating and the tank upgrade.
Naso's are different than most all other tangs, they are not nearly as aggressive, and can shy up at first, especially if the others are intimidating him as YT's tend to do.
Once they start eating that nori, you are golden IMO
Understandable sometimes we have to make do when it comes to rehomes/rescues.
I get a frozen mix food called five in one, and it has plankton, brine, bloodworms, squid, and vegetable diet, and it's processed in filtered water.
I add mysis to that mix as well.
NLS pellets are also great