What material will be featured in the city?
Stone bricks?

There is a way that you can tp on top of where you disconnected, by using locked doors (wooden) or trapdoors. I'm not gonna go into too much detail of how to do it for obvious reasons...
Is there any way this could be patched?
I saw a guest that knew how to do this, and he kept breaking into peoples houses and causing havoc.

So we better start making some respiration helm's then?

Do take into consideration that its harder to break blocks underwater, it's much darker, and you might drown?

Is the respiration enchant for underwater extended breathing?
Damn.. I had a helmet...

Yeah, Respiration is the only way to have extended breathing, but you could use glass panes for air gaps.

However, have you ever thought you could remove all the water, build the city then re-place the water?

I used to sell slime balls for $200 lol. But I haven't seen a slime in a long time.

Also I made a mob spawner like this:
http://www.youtube.com/watch?v=99B5IaLblCM

But because mob spawn rates are so strange at the moment I get no spawns in it...
A huge waste of cobble and wood (from all the trapdoors).

I hope it gets fixed...

So how much do good Silk Touch picks (Efficiency V Unbreaking III) go for?
30K-50K
How rare are Silk Touch picks?
14% chance at Lv 50
How many Silk Touch picks do you need to earn this money back
3-5

I mean on creative I enchant and enchant and enchant, more enchanting more enchanting and I have only ever seen one ever.

I would love to have a blaze farm, but it would take a huge amount of time to earn back all the money...

Oh right.

Feeling kinda bad now...