As a fairly new Shadowrun GM, I can't recommend
Runner's Toolkit enough. It's right up your alley, as someone that's still getting a handle on the system. There's a fun little adventure in there, there's a handy-dandy GM screen, compilations of tables and little reference sheets, and PACKs (which will be a tremendous help for making NPCs).
For myself, I'd suggest
Seattle 2072 next, but I'm a setting junkie. I can't help but suggest
Attitude since I helped write it, I guess, but I think for someone newer to the game either one would serve you well; both are chock full of setting information,
Seattle 2072 has specifics on neighborhoods and some Shadowtalk for plot hooks and stuff that are more Seattle-detailed,
Attitude is a little more of a "big picture" book that we tried to make a glimpse of just style and society (for Seattle or anywhere else). If you want more general feel and fluff,
Attitude, if you're looking for more specific neighborhood info,
Seattle 2072 is the way to go.
For adventures -- and maybe I'm losing the company money here, so no one tell Jason on me -- I cannot suggest the
Missions line enough (and I'm saying that before my pair of CMP's have been published, so it's not just stroking my own ego

). You can get a bunch of the adventures free on-line, others are available for like $5 or something silly-low, and it's got adventure after adventure, all ready to go. Even if you don't use the whole adventure, it's got some ready-made NPCs, some plot ideas, and stuff like that...great fodder for a GM that's trying to put together his own long-running campaign.