Flattening a stone can be done several ways with varying degrees of success.
The most practical is to get a diamond plate like:http://www.chefknivestogo.com/140grdistflp.html
Rub against the stone to flatten it.
Other methods involve 220 grit wet/dry sandpaper on a flat surface, rubbing against flat concrete, etc. But, the diamond plate is your best choice if money allows.
You should flatten often. You might think you're wasting stone, but you're not.
If you like the Moritaka a lot, get the 210mm gyuto from them:http://www.chefknivestogo.com/moritaka9.html
As you said, though, there are several other options.
There are some stainless steels like AEB-L that will take just as sharp of an edge as AS (actually sharper if you have the skill), and others that will hold an edge longer like M390.
There are stainless steels that are comparable in both departments to AS....like CPM154 (I'm going to get an argument with that statement....I said comparable
At the end of the day, though, get a knife that's interesting to you....don't buy based on specs alone. It never worked out for me.