Mini
There's the rub. As near as I can tell there really is no specific definition of what a 'National Crisis' is! Legislation was written to be vague in order to allow a POTUS leeway to decide that without getting bogged down by 'ticking boxes'.
Once again, we're faced with the fact that it was unimaginable to those who passed that law that we'd ever have a POTUS who would choose to so abuse those powers for personal gain and/or ego. I'm sure some may have wanted to (ahem, Nixon, ahem), but something (ethics? wanting to be reelected? fear of impeachment?) probably always held them back.
There are 2 'checks', the first is a joint declaration passed by Congress to cancel the NE but POTUS has to approve it. If he won't, the second 'check' requires a 2/3 majority in both Houses to override his veto.
The only real 'balance' I have seen is that Congress has to renew the declaration every 12 months to keep in in effect. For example, the NE declaration done by GW Bush shortly after 9/11 has been routinely renewed by Congress as it keeps certain funding levels active for spending on national security. The problem in the current situation is that POTUS would receive his $5 bil in one lump sum, rather than it being paid over XX number of years where Congress could stop it by not renewing the NE declaration.
This is a good article, but bear in mind that the US News & World Report is a 'right leaning' publication
www.usnews.com/news/national-news/articles/2019-01-08/what-is-a-national-emergency-and-when-can-a-president-legally-declare-one
(Thus endeth the Poly Sci lecture for today!!)