Also, in space size has nothing to do with top speed (unless some strange tech drive is used ) The biggest and smallest ships could easy hit the same speeds, Acceleration though . . that is the problem and that has more to do the mass then size. And ships will need to use energy to slow down also not something Naval ships would need to do . . Tactics then change even with these small differences. Battleships could match the speed of fighters if given an opportunity to build up speed A fleet with enough speed could blaze through a system too fast for even the fastest ship to catch (the main problems here is having fighting ships enter a similar relative vector “window” where they could get more then one snap shot off as they pass each other at crazy speeds) and so on . . . rather interesting stuff . .but all dropped for WWII.
Yep. Btw. you can experience this with some modding even in sins.
Just mod every ship so, that it has no max speed. No make it so, that acceleration and slowing down happens on the same rate.
Also mod the grav well to a larger size.
No, when two fleets meet each other, the following, quite interesting thing, happens:
Each fleet begins to accelerate. They get faster, and faster and faster. Some seconds before they meet, they begin to brake. Now half a second before they meet, they begin to fire at each other, a second goes on and the fleets are to far away from each other to shoot each other anymore. They still brake until they nearly stand still, they than reverse their course and accelerate again. They get faster, and faster until they again meet each other and fire some shots against each other.
(Unfortunately this doesn't really work with capital ships, usually capital ships will just ram each other, since they're too slow the avoid hitting.

)
It's quite fun, although it doesn't really work, since shield regeneration is too fast. You probably need to increase weapon damage tenfold and decrease shield regeneration to a hundred of the current amount, to make it feasible. But such a mod could be fun, fore some time.