Glad to meet another game developer!
Point 4: This is possible and something we've thought about, however the game turns (especially in larger battles) can take significant time and we're concerned that given the mobile platform, the game needs to be paced fairly quickly. Managing each turret individually would further extend the turn time.
Historically, ships fired one salvo at a time in order to measure the resulting splash distance to the target so as to build up a correct firing solution. The only time they would use different elevations would be if splitting their guns between different targets.