I'm thinking more along the lines of duel server. I've never actually fought anyone who switched attacks halfway throught the fight. Imagine fighting a longsword then getting hit by the 1handed leftswing animation. It would mess up my timing for sure.
1. You cannot switch the animation mid-swing, it takes some time during which you remain defenseless. It's fun though, I even use it on my 2h character with 1 1h wpf
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2. If you wanna go for a pure dueling build, I recommend either 18/21 or 21/18. Personally, after I switched from my 18/21 to 21/xx, I started preferring 7 ps, but 7 athletics and 7 wm could be advantageous as well.