Thanks for the kind words and the purchase!
If I can try and answer your questions -
1. The characters are assumed to be assorted good-for-nothings, survivors, hustlers and opportunists. If you are using the Backgrounds, that's what they used to do, or be, before they banded together as a group. Characters like this are hired because they're disposable and deniable. They do the dangerous stuff that bad people/orgs won't risk their preferred employees and assets for.
2. Jobs or missions usually come from someone who wants something. For example, a local Nexus may have heard about a drone going down in a rough part of the city and will pay the team to retrieve it for them. The owners of the drone will also be looking for it (criminals? a corporation?). What data is stored in the drone that makes it so desirable? The Nexus could use others to do the job, but won't risk valuable allies and won't want to pay much, hence contacting the PCs. The someone could also be a corporate representative or a criminal kingpin.
There's a little job generator in my Augmented Reality City Kit (which is PWYW, so grab it for free if you like). When I start a campaign, I always make sure that there's a few street-level contacts for the team who will want to make use of their skills for pay or favours.
3. The lore is scattered throughout the game text. The Backgrounds imply certain facts about the world, such as the existence of cloning technology, pop-up wars, orbital habitats, life extensions for the wealthy, robotics, androids and holography. The gear and augment lists suggest a number of dominant corporations exist. The Flow locations also suggest a lot about the world, albeit on a more local level, but there's mention of transhumance terrorists, foreign cartels, music scenes, hypermedia, gang wars, robot-cabs, etc. My idea was to supply just enough in the way of cool cyberpunk concepts to make the game buzz, but leave plenty of room for GMs to make worlds of their own - include the stuff you like and add in as much as you want. Any of the ideas in the game could be transplanted to a real-world location like LA, London, Pretoria, or Tokyo, in the dark future.
I hope that helps?