You can create Hero like Capital ships yes. They are close enough that it doesn't really take much. After that, the rest of what you ask is not possible.

Not possible? The AI is hard coded to need a few types of auxillary frigates like colony frigates, siege frigates, maybe starbase constructors. But beyond that there is no technical reason that would prevent you from removing all combat related frigates and just adding more capitalships.

That said TC, I do not believe such a mod currently exists. Part of that is because adding more than 9 capitalships to a faction is a pain, and any more than 13 or so would get excessively so. The Enhanced 4X mod explicitly has hero units, and others like Maelstrom have similar kinds of things, but they have not removed frigates from the game partly because Sins is the kind of game that is really cool to build huge fleets with and partly because most mods don't like to remove depth, though I do see why that kind of simplified play could be fun.

Edit: Now that I reread your post, it sounds like you meant only a Single hero ship. There have been jokes about making a Sins Moba before, and in theory it is probably possible as well, but I don't know how well it would really work. A less ambitious but potentially just as fun idea might be just making a custom map where all the player starts with is a titan and dead asteroid. That could be made in Galaxy Forge without any sort of mod.

Oh I know those are all possible. It was the mission running, researching, exploration concept he seemed to be envisioning IMHO that are not possible.

Again, to some degree they are possible, with some fancy ability work.

I do not believe such a mod is impossible at all, to some degree I've done all of the elements that would be required for such a system, though I have no desire personally to remove the RTS Empire aspect from Sins. However, there are two big style limitations that will get in you way that you need to be aware of.

1. Your missions will have to be fairly simple and only start on entering a gravity well. Sins is a Sandbox game and there isn't a scripting engine or anything to do things like check map conditions to do something. However, if you limit your missions to a specific planet, like "Destroy all targets at planet X", you can use Sins' ability system to do what you'd like.

2. The AI will have no idea of how to handle this kind of setup, so that means you'll basically be spawning custom militia groups, which will only hang out at the planet you spawn them at. This means that nothing can really chase the player around, so the player is free to go where he likes with no threat until he enters a planet with a mission.

Cool, hope to see you online sometime.