@GreyGhost let me see if I can answer:
1. pretty sure the solid block walls can support another level.
2. Yes, only get rid of the roof atop the current living area (lower side) and have 5 living levels instead of the current 4
3. No cantilever, just straight up
5. would like a balcony/terrace up there depending on available space. Even a small 3-4 foot walkaround.
6. Also an option, but will have to see what type of values we'd be looking at. I assume 1.5-1.6M selling price for ours in current conditions. Leaving us with about 1M in cash toward the next purchase. Mortgage agent said 500k is max mortgage, so this option is unlikely.