So I watched TheMap's terraforming video, maybe multiple of them, who knows, and it got me thinking of a couple questions.

1.) If you dig down, when there is no water around, will the space fill up with water, i.e. default when group is below ground level
2.)With D represent dirt and / representing a log
DDDD
D....../
D...../
D..../
D.../
D../
D./
D/
D
Can I add dirt onto the log in open space if there is no dirt underneath? If yes answer next question, if no, ignore.
2a.)Can a log go from point (0,-6) to say (1, -4) or does it only allow certain angles?
3.)How high can you build?
4.)How long to do each improvement?

Ok, reason I ask is that I want to, in my head at least, create a dirt wall surrounded by a pit accessible by a log bridge being say 2 or 3 logs long. If ground dug under ground level fills up with water, then that plan won't work. Oh, did I mention somehow filling the pit with vicious [spoiler]"Go for the eyes"[/spoiler]

Thanks in advance, and yes, I know it's insane, but, hey, maybe I'll finally be able to create my own secret lab, errr....ignore that