I bought a couple of fortresses yesterday. All good so far. You need to fix the english on the auction place:
"Steps in 0.1 ether If already bid, it increases your bid". I dont really know what it means.

You also write "How many fortresses are available? The first limit is 1000. After some testing I will enable the minting feature, which releases a new fortress every 15 minutes.".

I think it's impostant to have a game plan ready, and by the looks of it, you already started this. But doing this Cryptokittie style aint gonna work, unless the price goes up for every fortress bought, of course.
If you keep a flat fee (i.e. 0.01 eth) for every Fortress built, people will stay on the fence and not start up until they see that other has started. Therefor it will never take off.

And yes: I enjoy so far. Cant wait for more features!