1.Force Dice. Does each player roll it at the beginning of the game, or is there only one rolled for the group that everyone can use?
Every Player rolls, this forms the Destiny Pool.
2.Advantage and Threat. Can you spend advantage on the turn that you rolled it or does it have to wait until next turn. If you have to wait until next turn how do you track it? Having 4-5 players while I GM a new system will be very difficult to track something like that.
You spend them during the check that generated them. They are not saved. Symbols not spent, are gone forever.
3.Advantage and Threat. Does it have affect if the inverse happens? For example, if a PC succeeds on a roll can the GM still "spend" the threat dice to hamper them? Or is it only if a roll fails? (And vice versa)
Typically Advantage/Threat/Despair/Triumph are independent from success. So, say you wanted to try to convince someone of something. You roll deception and succeed, but with threat. The character believes the lie, but maybe is suspicious of you and could be angry regardless of the belief.
4.Boost and Setback. Are these purely situational? The rule book gives the example of trying to pick a lock under fire gives you a setback, but does having a lock pick give you a boost? In other words, can these be given for having proper equipment?
100% situational. To the lockpick giving a boost, that is up to the GM, but is not inherent to the lockpick item.
5.Boost and Setback. Do they cancel each other out, or are they all just added? If you have one boost and one setback do they negate each other?
They do not. Potentially the symbols generated could cancel each other but you can have multiple of both.