First, allow me to suggest you pump Dex as well as Str. The defense boost you will get from Dex is invaluable as a S&S warrior, and it also helps minimise those misses. Also, it seems you're trying to go DPS with a S&S, and frankly the two aren't a great fit. I mean it CAN work if you want it for role-play reasons or whatever, but if you're going for maximum efficiency builds, a S&S warrior will never get the big numbers like a 2-Hander.
1) Champion is the classic S&S spec. Crowd control and melee buffs/debuffs - just what you want. For a secondary spec, Berserker will certainly boost your offensive abilities, which sounds like what you're going for. But Reaver is worth considering as well, particularly for Frightening Appearance (because you'll be wanting to draw all the aggro) and Blood Frenzy (because your health pool should be relatively stable).
2) Frankly, besides Shield Bash, there's not a great deal in the S&S tree that's amazing for damage. It's all rather defense based. It's all about drawing aggro (Taunt and Threaten from the warrior trees) and then keeping yourself alive (Shield Wall is your best sustainable). You'll be auto-attacking a LOT. So maybe you'd like to invest in poisons to keep your blade as deadly as possible and/or bombs to keep things interesting...?
As far as Leliana and Zevran go, the AI is actually a bit hamstrung when it comes to DW rogues because you can't tell it to go for backstabs, which is where DW rogues excel. However, this all changes with the acquisition of one talent - Coup De Grace. Suddenly your rogues don't need to be behind an enemy to get a backstab - they just need to stun or paralyze them. So once this is acquired, set their tactics to use Dirty Fighting and Riposte as often as possible. Also, you'll want Momentum on pretty much constantly, and the first three talents in the Dual Weapon Training tree are must-haves. You'll also want to get Lethality and pump their Cunning sky high to get the big numbers. The Bard tree is kinda useful (though not essential) for Song of Courage, while the whole Assassin tree is pretty awesome.
3) Yes you can.
Good luck.