Do I need to support the ceiling (interior wall removed)?

[finntrollet]

Will install flooring similar to what is in the large room.

Vprör was for an electrical outlet that was in the previous room, went to an outlet 2m away where it was connected.

 

[hrt]

If it's just concrete, then it might work to level it with self-leveling compound so that it matches the height of the slab. But I would have removed the old (white) floor first.