Welcome to the boards, Mkichjr! I can't speak for everyone, but I do actually still make plug-ins for my own use from time to time just for fun. I'd be glad to help.
I believe all three things you want to do are in fact possible. For the first, do you want the mission to be offered by a ship or from a planet? If the former, simply make it identical to what Nova has; a përs ship offers a mission which auto-aborts, pays the player anyway, and removes 1 jump's worth of fuel. The exception is that përs would always show up in the system you want the mission available from and always offer the mission when hailed. If you want it offered from a planet, however, I'm not 100% certain that would work. I've never tried nor have I seen it tried elsewhere. It's a simple test, though. Just make a mission that auto-aborts, pays the player, and takes away a jump of fuel and is offered at a specific planet. Go in-game, accept the mission, and see what happens.
The second objective is very simple, if you are working with Nova's engine. I'm not too certain how to accomplish this with the EVC/O engines, unfortunately, but with Nova the various cargo types are dictated by STR# resources. Specifically IDs 4000, 4001, and 4002. ID 4000 gives the full name for the cargo, 4001 gives the same name in lower case, and 4002 gives an abbreviated name. Simply go into the resource, add a new line, and put in the name for the cargo you want. Then have your mission's cargo type set to that number. Keep in mind that the cargo type field in the mïsn resource starts at 0, but the STR# lines start at 1. So if your cargo is, for example, listed at line 50 in the STR# resource, then the mission would need to point to 49. Just subtract 1 from the STR# line to get the mission value.
Objective three is also fairly simple. Make a weapon which destroys the parent ship when fired, and put -1 as the values for both its firing sound and sprite. Make sure the ship you want to explode upon entering a system is equipped with it. Since only AI ships will use this weapon, you don't even need to make an outfit for it. Then make sure the ship will want to fire this weapon at someone in the system. Give it an insanely long range so it'll fire almost no matter where its chosen target is. You could even just make the ship belong to a xenophobic gövt so it attacks the player immediately. As soon as it fires this weapon, the ship will explode. Since the weapon has no sound or sprite, the player won't know a weapon was fired, and the weapon won't even be capable of impacting and doing any damage or even making another AI ship aggressive.
If you need me to explain any of these further, or have any other questions, please feel free to ask. :)/>
Thanks DarthKev.I'm still getting a hang of the EV Override plugin maker. Is there any program other than mission computer available with a good gui?