Right, all items are very sensible. With these nontrivial changes, I'd prefer you to implement them.
I'd include one hatch-exit distance per player count, not all possible distances.
Also consider: Use a thicker diggable floor. To prevent hatches from merging with each other, replace some of the diggable parts (between hatches) with steel. Source for this suggestion: Silken didn't see that the floor was diggable at all.
-- Simon