As fas as your concerns about free diving after scuba diving, decompression illness from breath-hold diving does occur. Of particular relevance to the sport diver is what happens to the snorkeling breath-hold diver who repeatedly dives during the surface interval between scuba dives. Very little nitrogen is transferred from the alveoli to the blood during one breath-hold dive. If you go snorkeling between scuba dives, you should stay on the surface. I read that asthma sprays can cause air bubbles to go from veins to the arteries and could cause embolisms.
Scoliosis varies considerably in the extent of the curvature.
Some cases are so severe that the chest cavity is distorted and the affected person can have abnormal lung function. Another concern would be possible injury to the spine from lifting heavy weights and tanks. You will likely have more difficulty with gearing up, entries and exits, but this difficulty disappears in the relatively gravity-free environment of the sea. The advice of your personal physician should be sought with these factors in mind.