@Fate: I've got a couple (semi) answers, but I'm not too knowledgeable about a lot of this stuff, so I'll just skip some.
1-Space Mines' "self destruct" (if I remember) has an area of effect. I think Aezeal meant for them to hit themselves, but it doesn't seem to work out that way.
4-The power level of assassins in the mod might be due to most nations being, in Aezeal's own words, rather more powerful than your average Dominions nation.
5-Once again, nations are generally more powerful in Dom3K than Dom3. Though, I guess a thug in Dom3 would still be fairly powerful in Dom3K.
6-I think that was from Amos's original mod, actually. He suggested it for thematic reasons.
Oh, hey! Johan K, developer extraordinaire, is here! Let's see...
@the tank: Yeah, the frame around the tank hero is weird. Hopefully it's easy to fix, though.
@forest-vs-space: I think we settled on forest because water was coded to act like water, not space. Units can move 1 province/turn in water, period, which was a really big disadvantage. Sailing could've been cool though. Still though, the 1-move limit plus the lack of blood hunting sort of nailed the proverbial watery grave for water provinces.
We wouldn't have to use either, though, if you let us play around with void terrain and voidforms!