1. Quest rewards, puzzle rewards, various mobs (in dungeons and out), and PVP chests/towers can be good sources. Consignment also sells them.
2. You can get them rarely outside of dungeons, but the good ones (the ones that need certification) are dungeon drops. If you're not keen on dungeons, Consignment can be fairly cheap at times depending on your class and what piece you're looking for.
3. Yes, rare or better equipment and weapons can be taken to the Salvage NPC to be randomly salvaged into cyberclusters, enhancement stones, passcards, or pet food.
4. Accuracy, Chakra-Attack (this is the damage that appears in colored numbers), Evasion, Chakra-Accuracy, Chakra-Evasion. You can read more about stats here
5. Selling drops to other players mostly. Dungeons are usually fairly reliable for income, provided you have the passcards to spam them. Or spend AP and resell the cashshop items to other players.