The 'brown bomber' could be a symbol of strength or protection in the love story. Maybe it represents one of the characters who is seen as a protector in the relationship, like a boxer (since 'brown bomber' was a nickname for Joe Louis, a famous boxer). And this 'brown bomber' character might have had a special dinner to show their love or commitment.
The Qinglan water bomber was a water bomber developed for the I-400 submarine. It could be folded to fit the needs of the submarine. Qing Lan's combat mode was a surprise attack or sneak attack. The way he appeared was described as smoke in the clear sky. It could be mounted on a submarine for strategic use. Qing Lan's main weapon was a Type 93 machine gun, which could also carry 800kg torpedoes or aerial bombs. Qing Lan's design and appearance were similar to the Comet Bomber. However, due to Japan's defeat, the plan of the Haruhakan water bomber was not realized.
A 'bomber novel' could potentially be a novel that involves bomber planes in its plot, perhaps set during a war where bombers play a significant role, like in stories about World War II air raids.
I don't think so. There haven't been any official announcements or indications that the HxH manga will continue. But you never know, maybe there'll be a surprise in the future.