A few more Newbie Questions & some Observations..

[Krsqk]

As oleg said, if you destroy a target and still have unfired weapons, you can choose a new target--especially useful against fighter stacks and smaller ships. Point-defense weapons do not count toward the multiplex limit.

When you fired at max range targets, only the weapons capable of firing at that range fired. At medium range, any weapon which was left and could reach the target fired. At short range, all remaining weapons fired. This is why you saw the multiplex effect at different ranges. I have no idea if the AI (strategic combat) will make use of multiplex tracking.

If your projects don't require all the points you are generating, ADD MORE!
All the extras will spillover into the next project.

This is the best advice I can give. If you divide points, any points contributed to a project which exceed the amount needed to complete it provide no benefit. Eg., If you need 15000 points to research Projectile Weapons lvl 3, and you are spending 25000 on the project because of divide evenly, you effectively lose 10000 points. It is better to line up several projects at once to use up the excess, and leave "Repeat Projects" on.