1) Good question. I have three answers! a) The answer depends on context. What kind of gang is it, what's the character's relationship with the gang and its members, what do both parties consider a "fair price". Remember that a gang is a group of people with individual desires and needs. But overall, it will depend on how the fiction has been established at the table.
b) It might be that payment to a really close Contact, like your own gang, comes in terms of favours not Cred. Certainly if he's just wanting to borrow things, that will cost less than buying them.
c) Magnetic has believers, right? He should use Vision Thing on them.
2) Yes, the gear that +gear produces is as permanent as any other gear the characters buy. Exactly what you can produce will again depend on the context. In the discussion it says: "you can only produce equipment that you could reasonably have in your possession or could have been relatively easily obtained." What counts as "reasonably have in your possesssion" or "relatively easily obtained" depends on the style of game. The answer will differ between the game that focuses on low-level street bums in a semi-apocalyptic industrial wasteland and the game where the players are a team of ultra-professional trouble-shooters on retainer to a megacorporate executive. It might also depend on the specific mission. If the entire mission has been spent in a high security orbital environment it might be implausible to have brought in projectile weapons of any sort, but the automated electronics factory they hid out in before the Action phase might mean that programs and even cyberdecks are available.
Personally, I would tend to restrict produce gear to things that cost 2 Cred or less (more complex restricted gear from a fixer -- grenades, assault weapons, legal drones, basic hacking programs). Remember also that the player has to narrate how they got the gear. That might include buying it, in which case they should pay for it in Cred or favours as appropriate. It might also include stealing it, which might result in enemies.
Thanks for those questions, Kuzco. Some of this will definitely end up in the document!