LINK - or any information exchange is needed if you want to make multiplayer mode with cooperation option - where two players controls own warship/submarine and have different sensors and abilities. For example submarine player haven't the same "surface" situation picture like warship commander.
If multiplayer will be only 1 vs 1 link is not needed. But i think most players would like to play with team vs another players team.
For me best solution would be assigning roles. From battle group commander (where player controls own unit + every AI, to warship commander - where player controls only ownship
About time acceleration:
In my opinion it depends on maximum scale of battle. If map size will have thousands kilometers it really have sense. But i think scale shouldn't be so big. For me better solution than "slowest requested speed" will be automatically time managements. For example at beginning of battle both sides havent enemy contact and game would run x2 or x4. It allows to move own forces to key strategic points or for better tactical planning. After detection or some speciffic events (opening fire etc.) game will change time compression to x1.
It will eliminate situation described by @Herman
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