1) Totally, not worth it. Just a waste of time.
2) There is no chance to sell wow gold in private servers. Though, there are a lot players ( in official always ) who buy big ammounts of gold and totally worth it to sell.
3) Daily quests or quests generally, and professions. With professions ( depends on what you chose ) you can gather mats such as stones, herbs etc and sell them on the Auction House ( A place where all items are being sold in different prices. )
4) Not.
5) Depends on the realm. There are realms that are 90 % alliance and 10 % horde but there are realms that are 90 % horde and 10 % alliance .. etc etc.