As far as I know damage increasing sigils only work with the weapon skills gained by the weapon they're equipped on. So if you've got a sigil of outlaw on your main hand and a different one on your offhand only your 1-3 skills gain the 10%.
As for if it stacks with a potion, I would assume yes.
dungeon finder was not introduced into mmorpgs until wrath of the lich king in wow, that was not too long ago. prior to the introduction of dungeon finder, players had to make do. GW2 is not at this stage in development, try and make do.
Prior to that however WoW did have a decent grouping tool, where you could select which dungeons you want to run and which was displaying you along with anyone else willing to run w/e dungeon. GW2's LFG tool is just terrible.
so im assuming this is not possible with the, "double tap key to dodge" function right? im just not following this, you double tap "D" for instance, and spacebar at the same exact time? you'll jump before the dodge command kicks every time.
You shouldn't be using the double tap dodge in the first place. It's terrible.