Rogue DW / BS question

[Beldon]

I have a few questions on this one so hear me out. I also apologize that I cannot test this right now as I am at work.

My rog is about to hit 10 and get Back Stab. Shortly after that (13) I will get Dual Wield. Currently I am rocking a Fine Steel Rapier and just picked up Whip of Strangulation last night.

I get that I will equip the Rapier - sneak up and BS the target. Then I will equip the Whip for the rest of the fight. My question is can I still "use" BS during the fight? Will it just count as another attack that could proc the Whip?

When I do get DW, I might be able to get a 7/22 1hs I believe. Am I better off using the 7/22 as my main and Whip as my offhand. Or will I have a better chance of getting the Whip to proc by placing it in my main hand? I am pretty new to the DW skill, so please forgive me.