First let me say that the proposed warrior build is/was meant to be extremely newbie friendly.

As to your questions...

If you are going to do daggers as a warrior, I highly recommend that you start with that as your 1st spec. The damage you take on failed skills is proportionately lower, so your able to practice them much more effectively. Additionally failing them in PK is a lot more of a problem at hero than at level 30. I could tank with my arial dagger spec decently pre-40. This gave me a long, long time to get concealed up. Had I taken it as my 2nd spec, I wouldn't have been tanking.

Arial spear/staff as 1st spec kinda bores me all the way to level 40. There just isn't a whole lot of offensive stuff going on... just impale, crescent (about as fun as kick) and misdirect. I guess there are edges now, but... meh. "Your mileage may vary."

If I were going to do dagger/spear I'd take spear as my 2nd, so that I could keep tanking all the way to hero. I would surmise that an arial spear/staff with dance could solo relatively easily all the way to 51.

As to your legacy choices, stsf/dance is like... well extremely popular. "Cookie Cutter" might be another way of putting that. That said, if I were going to do those legacies and dagger I'd almost certainly take flail as my second spec. Mace would be my second choice.