Since it's finished on the top levels (until I decide to add to it), I figured I'd take some pics of what I've been working on.... It's sort of evolved with no real plan...
I'd started out in search of lapis... so I wandered off and stopped when I saw the newer white trunked trees, and knew I was in newly generated chunks. I'd also found a large natural crevasse, so I built a tall tower with 3x3 platform above it and a ladder extending down into the cave and would hide up on the platform with all my stuff when I wasn't mining or off exploring. Then I realised the shadow of my platform was keeping the mobs alive in daytime, and making me unable to get down from my secure tower, so I had to build it from glass.
Then I got a bit sick of there still being creepers circling the tower trapping me up there, so I decided I needed to build a safehouse around the tower - with doors on each side so I could lure the mobs to one door, and escape out the other..... and I decided it was best to seal up the crevasse, because I was sick of falling into it as I was running away from mobs.... and that I needed to clear some of the surrounding forest so I would stop being ambushed by creepers and being chased into the aforementioned crevasse... and perhaps a nice safe impenetrable wall...
So it ended up becoming this:

(which actually looks like a big mess in this pic lol)

(One corner)
I really wish I'd taken some more photos of my progress...

The top of the wall/walkways on the left was on ground level. Then I dug down a few blocks to stop mobs climbing onto it, and then had to dig down more to stop creepers hiding under it and blowing it up as you walked over .... So then I decided it was going to look better if I flattened the lot... I had to level it down almost to the centre, and there was anther (half as high) hill on the right side too that needed to be levelled. Which involved a LOT of digging ....
But then I had to build up the land on another side, because it was far below the level I needed. And I had to pack it up in layers, so that there was no more than 1 block high space, so that I don't have mobs spawning in the ground... I ended up having to level out the ground outside my walls too, to get enough dirt to fill in the holes inside my walls!

This shows the section I had to build up (level with the top blocks on that path), and because I decided to make passageways underground underneath the above walkways, I had to build that into the low side too
Of course, as I was desperately trying to make nice smooth lawns, I kept getting creepers undoing my work!
But.. I finally got it done!
All the walls have fence posts every second block, to stop spiders climbing up. The water channels also keep you 3 tiles from the wall, which means if there is a creeper against the wall in the grass area, you can be safe on the walkways because it won't blow up. Each hole in the lower walkway walls has a torch in it, which stops arrows... so it's completely safe to walk around the walkways at night. Though occasionally something will spawn up on the top walkways, as there is less lighting up there.

(From the top level looking down - the walkways all have glass in them, to limit shadows)
The central building (on ground level) was the original safehouse to protect the base of the tower - prettied up a bit.
Going down a level you come to some underground walkways that go directly below the upper ones - with a glass block row in the ceiling to let light through

(gah - uneven torch placement! will have to fix that)
I did have a central pillar with a ladder, but I realised that blocked the view right down the underground walkways, so I've changed the ladders up to stop that. I've now decided to connect the walkways around the edges too, so that they follow the upper walkways right around the edge of the wall.

(still under construction)
Which of course means digging out along one side where I'd painstakingly filled in before

Also because of the way the water channels go, the undergound walkways actually extend 2 blocks outside from the wall, so I've had to go and put back a lot of the dirt I'd cleared from around the outside of my wall - because the underground walkways would have been exposed.

And I have to make a HUGE AMOUNT of refined stone to pretty it all up.. so still a bit of work to go there.

(Underground walkway section dug out, just needs to be prettied up)
And... I've just added what's supposed to look like a flower... on the top. It's smaller than I'd have liked, but it already took nearly 3 stacks of purple wool per petal! So it'll do