Is it okay to use lacquered doors for balcony doors?

No, there are three main types of lacquered doors, molded doors (the inside of the door is filled with honeycomb paper), composite lacquered doors (partially filled with wood or other material fillers), and solid wood lacquered doors (there are pure solid wood that is consistent inside and outside, and solid wood inside and out, but the material is different). Most of the doors are made of wood or other wood materials, and the amount of water content determines whether it will be deformed, while the wood of the locally made doors is consistent with the moisture content in the air, which can avoid quality problems such as deformation in use.

Lacquered doors don't have to be solid wood composite doors. >>>More

Usually there are exhaust vents in the dark bathroom, if you use the whole bath, dry and wet separate, there is no problem, if you are not using the bath, it is best to use plastic steel doors, which are more resistant to humidity and can be used for a longer time.

There is no problem with lacquered doors for geothermal rooms, and solid wood composite doors perform better than pure solid wood in terms of heat resistance and thermal expansion and contraction. >>>More

Yes, of course, the thicker the insulation, the better. It is best to use insulated extruded plastic boards.