If it's something I'm going to use at some point, I always keep it. It's not worth having to go find or buy more later for some quick cash at the moment.
Oh yes higher level mobs can be dodged by just standard strafing/jumping. It requires better timing, but it's certainly possible. I do it constantly 😛 I spend basically all my time in Orr now, so yeah. Believe me, it's possible. It's just not easy. But it's very possible.
And it should work; I've done it before. Click the person, right-click their name/picture, and Invite to Party usually shows up.
As far as that goes, I haven't messed around with the Forge too much. Four rares/exotics gets you chance at one of the base exotics that you use to craft the legendary weapons, though.
Speaking of exotics, I really wish that the drops you get in-game line up better with what you're playing. I've gotten exactly four exotics so far. Not a single one was something I could use (and the two I got today were so crap that they only sell for 40s on the tradepost!). At least I actually got some damn ecto out of them when I salvaged - I now have enough for two pieces of exotic armor. Now if only I could get enough gossamer...