The Impulse activation should happen automatically once you unlock your D2D copy. To me I do find it worth it, as it means you have two alternatives to download your games from instead of just one. If one company goes out of business (doubtful, just saying) then another one is there to pick up the slack.
As for GFWL, DoW2 ran the same way pretty much, only Steam handled the backend of that a bit more. Two GFWL accounts cannot be logged in at the same time as far as I am aware.
Not sure about conflicts otherwise though. DRM exists in the form of GOO by Stardock, and I am not sure what their specific checks are for each activation that would cause an account to get flagged.
[quote name='Reaperain']btw a post on here said that you have to 1. Download 2. Install and then 3. Activate the game using the activator with your impulse email and then you can activate it on Impulse.[/QUOTE]
That's correct. I tried using the key before activating my D2D copy, but I kept getting denied. After installing the D2D copy and activating it, it was already listed in my Impulse games list.