A quick plan:
The lowlands are bigger but they were sparsely populated compared to the others.
Slavonia - Zágráb or Zagreb. Eszék wasn't part of Slavonia.
I strongly suggest Buda, Pécs, Várad, Gyulafehérvár as setlements.
I would put Székelys and Saxons to East Transylvania including the lands outside the Carpathians. Center might be Szeben or Brassó, as you wish.
In the case of the northeastern province with Várda - I suggest Kassa as settlement.
In the case of the Csák territory I signed Trencsén, their main castle. Nyitra is good, too, it was the center of a Bishopric. Pozsony would be good, too, but it's too close to Wien.
Severin is Szörényvár in Hungarian, the name of territory is Szörényi bánság.
Csanád might be the center of the big southern province. Szeged is good, too.
Várad province should have Cuman local units after 1243-45. The exact return date is not known. They were important in the later wars.
I'm not sure about Wallachia. It would be very small because Hungary owned its significant parts.
Division by the domains of oligarchs might be good, too, however 1237 is too early to represent them as rebels.