This sounds like an absolutely awesome mod! I wish you the best of luck with it.
Do you have any plans to add new alien races or ranks?
Working on diversified ranks now, no new races until someone introduces some. None of the UFO races really fit the theme.
Basically, I split the aliens into combat races and science races. Gill and Lobster Men tend to be more frontline, Aquatoids and Tasoths are squishier, but can psi attack, even the rank-and-file, though with varying degrees of power. Psi LOS is strongly encouraged, though.
Mines have a detection radius which covers all 8 adjacent tiles. If someone steps inside, the thing goes boom. I guess you could make them less than ideal by limiting blast radius to 1, so if someone steps next to the mine diagonally, the blast will not touch him.
I'll probably set the radius to 2. I do need to address explosives in the early game, though - grenades are pretty overpowered against gill men and aquatoids, so it's fairly easy to spam them. I might have to nerf throwing accuracy for starting soldiers or, once different soldier types get implemented {or documented?}, I'll probably implement hiring of specialized troops.