Eh yeah, the side engines are too low. It's because of the refineries, and also because when I started building it, the design I had in mind was very different XD

Nice space elephant, dude)
Though thrusters could be put more realistically.

Yeah I tend to have those as well on most of my ships and stations :D I'll post another thing in probably a couple days, if I manage to finish it, it's a mobile station, and it has quite some of those secondary passages :)

I was thinking more of the thruster movement speed. But I guess the extra mass also helps avoid getting pushed back from the asteroid by the piston drill too.
Sure you don't need access, but it's fun to have little access corridors everywhere.

Well the heavy blocks are the outer hull points; they act as "bumpers" in case of collision. Also it doesn't matter if they're heavy: the ship is already using only 10% of its gyro force, because the pistons in the mining probe would bend and fall apart if you turn too fast XD Man, I hope they're going to fix the pistons soon.

Also, well, you don't actually NEED access to the lower deck; there's not much space left to begin with, and every function can be remotely accessed.

The double-extending drill is pretty cool, and I really like the combination of glass with the old-style windows. Will have to use that in future :)
If I were to make any changes it would be to replace the heavy armour with light armour. The heavy blocks on the main ship aren't really protecting anything, and they're heavy . The heavy armour on the drill head I'd keep, as that takes a beating no doubt.

PS you could probably fit some access stairs to the lower deck from the rear of the upper deck if you remove the blocks behind the side solar panels