The white residue on the leaves looks like mineral salt deposits left on the leaves when they are misted or sprayed with water, fertilizer or pesticide. It is harmless.
Outdoor light is much more intense. If you move it outside to anything more than shade, the older leaves will not be adapted and you will lose even more of them. You will have to move it back inside soon anyway, so I suggest that you keep it in the sunniest indoor location that you have.
The leaves you have lost so far could be from a lapse in watering or simply because it simply has reached the maximum number of leaves that can be supported in that light. Pruning back some of the longer branches will help it preserve the older leaves and keep it more compact.
Don't water by schedule. Water it thoroughly as soon as the surface of the soil feels dry. If new leaf growth is healthy, then you are on the right track and no major changes are required.
