Are they wanting to move the capitol south to protect it from a response to their own aggression? Does that reveal any kind of timeline?
BTW, would the artillery density be enough to blow a quick path through the minefield?
As to the second point: Well, I'm no "cannon cocker" but I think that artillery technology and munitions have grown so much that "counterbattery" fire is near instantaneous and effective. Current doctrine is to shoot and move out, fast! I don't think that lends itself to blowing holes in deeeeeep minefields. There would also be a variety of obstacles employed including tank trenches and the like. It would be a patterned, layered defense in depth with overlapping fires from both tac-air and helicopter gunships using standoff tactics and special munitions.