2) It benefits society because you no longer have to work to live. This affects how you make decisions about your employment. You would be more likely to change jobs when you're unhappy, for example. This is good.
3) Whether you make $40k, $100k, or $500k, the $10k isn't there to prove "additional income support". The system could be set up so that after basic income is implemented, your disposable income is the same as it was before--people making $40k wouldn't have $10k in free money to spend, because their taxes would go up $10k a year, for example. The key here is that if they choose not to work for some period of time, they can. That's not how I think it ought to be implemented, but the principle is true.
4) If government handed out $10k to everyone, they could tax everyone $10k and it would be like nothing happened. The difference in implementation would be that the additional taxes would be progressive, while the benefits are flat. So if you make over $100k a year, you might be taxed $15k more than you were before, but you would also receive $10k. Without a doubt, an effective basic income would require a more progressive tax structure than what we have.
5) "If you do start to add guidelines for poverty, etc.," not familiar with this reference, but presumably a basic income would eliminate extreme poverty. Do you mean like, for example, what would someone who was physically incapable of working receive? Is the basic income enough?