Does he have the forces to launch a full on assault. Yes.
Does he have the logistics to support lines of supply for an extended assault: Unknown
What is his primary objective if he DID invade: This is the kicker.
What is his main target - and if he is NOT able to maintain a prolonged assault, then it stands to reason he is after short term goals in the least possible time...which indicates to me (Im an untrained armchair tactician, I know, but this is a good guess) that whatever he is after if he invades, he has a good prospect (to him) of seizing and holding it for at least an appreciable length of time.
Get in fast, grab it, seize it, hold it.
He is well aware that a prolonged attack will eat his supplies and ammo at a logarithmic rate, and his generals know this too, so this points to a possible lightning attack using overwhelming force to seize and hold either a/ a beachhead he will dig in and fight for (this is bad as an entrenched enemy will be hard to dislodge) or b/ a specific objective that will be great value to his enemies, and may or may not be a hostage city / area which can then be used as a bargaining chip.
Thats where the demo nuke may be the key element: do as he says or the hostage gets it. Thats the nightmare scenario, especially if the zone is in Sth Korean territory.
C / he has to have at least one or more secondary objectives for the attack, and I am hazarding a guess that these will be bridgeheads he can use for supply, command and control.
I am guessing, but from a military point of view, if he gets into an extended slugfest he will lose overall, as the first Korean War will attest.
It is more than likely this is sabre rattling and he has an ulterior objective, aid, financing, food, supplies, easing of embargoes...but to me one thing is obvious. China will be drawn in whether they want to or not, and he may be looking to use them as leverage. A role the Chinese can do without.
I am in no delusion as to the failings and inadequacies of his forces, as compared to modern day armies and their technolology and air power. He knows it too. I am hoping I am wrong and this is all a bluff.
It would not be beyond him. My gut says there is more on the table.....just what, I am damned if I know.
And it is also possible that he isnt the one calling the shots.