1. I agree. A cosmos space should be 0 height & not placeable on any other tile.
2. I like it. Maybe for non-flyers, half their movement value & only in a straight line.
3. Tough thing to equate here but I think that is the best simplest idea. I'd only be leaning towards maybe 2 auto-wounds for non SS figures & 1 unblockable die for SS figures.
4.
Rock tiles for stable places in space. Maybe the movement is restored, but the "harmful" space rule still applies.
Special tiles for asteroids/meteors with special movement rules (like a directional pointer & a speed -either per turn (fast), per OM number (medium) or per round (slow -relatively).
Grass & dirt tiles for atmosphere where the neither rules apply.
Need an industrial tile for things like space stations/ships/structures.
5. I don't think this is necessary. Just complicates things. However if you want make asteroid tiles on stands that should definitely be a LOS blocker.
Nice ideas.