How you put the dimensions of the room and the pointers for the doors??
In each room there's a button "Copy room pointer to the clipboard". After copied you can paste it on the new door that you'll make (Paste in "Dest Room". You can too edit the door to put the area of the room it takes if the room is bigger than 1x1
About the dimensions of the room: Edit them direct in dsvania. Select "edit layers" and you can change the widgth and height
The game reuses tilesets so I guess you need open the desired room and to copy the values shown in tileset editor, then open the room to modify and paste said values, in this case only GFX list pointer and Palette page list pointer are different. I had a lot of problems with that while modding PoR, I had to refresh and apply every single time, that was in a old version tho.
I modded the starting room with SotN graphics, then in Chaotic those tiles reappeared all messed up.