Federation Commander

I'm not sure if I understand rule 4J2e correctly.

Is it saying that on the first turn of the game (unless stated for a written scenario) that plasma launchers larger than type F have only one turn of arming done so that those launchers would not be able to launch plasma until the second turn (except for 2 turn F)?

Do not plasmas get the ability to empty batteries and complete arming on the first turn that all the other multi turn arming weapons get to do? That would put them at a big disadvantage at first.

no they dont, as most other multi-turn arming weapons are only 2 turns to load but most plasma apart from Fs is 3 turns to load so giving plasma the chance to burn batteries for this would be overpowering.
it does mean you start with batteries though

That being said, all non-F batteries are still able to fire a two-turn "F" as they're called. So you can fire all your plasma weapons on turn 2, you just cant fire anything bigger than an F. (and maybe a D? Not sure about those as I don't have the rules)

Plasma-D torpedoes don't follow the normal arming procedure. Instead, they're 'activated' using a 'pay per shot' process. So yes, they can be fired on the first turn of the game.

This is indeed the case - type F plasma launchers begin the game fully loaded as the torpedo is held in a stasis box and is therefore able to be kept armed. Type G, S and R launchers get their first turn of arming paid for at the start of the game if they wish to, much like other "multi-turn" weapons, except that they start with full batteries - this is presumably to help balance the fact that a full-strength torpedo will not be available until Turn #2, as you say.