Great apartment. You are 5 minutes away from Gran Via, metro stations and entertainment. One of the attractions in Madrid is to sit on the plazas and you’ll be able to enjoy quite a few while you stay here.
We were a group of 4 and am positive you could fit 5-6 people here as there are two small beds in the living room and a sofa bed (although this sofa bed needs something to keep it fixed to the wall as half of it separates from the couch).
Madrid weather was quite chill, we didn’t have air conditioner but fans worked good for us.