When all water is in gaseous phase, around 400K (126C or 260F). So, we should expect sulfuric acid and other similar gasses to appear in the high in the atmosphere, creating invisble clouds and giving the gas giant a lime tint similar to Venus. Terraforming such a planet would be a difficult task. we would have to remove the atmosphere and cool the planet down with such needs. the sulfuric acid would burn skin and explode with water. so if building a sky city, we have to be careful. the pressure on the core would be immense aswell, so maybe it could have a strong magnetic field. moons would be unlikely as they could easily be flung away.