I'll try to help a little with your questions, but I know there are others here who can be more thorough:
1. This differs with everyone, but I can tell you that it WILL happen (feeling like you can eat normally again). Even though it doesn't feel like it could possibly. However, realize that your teeth/bite/etc. will be changing for the entire time you've got your braces on, so there may be times you will feel totally "normal" and other times where you'll feel like you're back to square one. Again, this is part of the process. :)
2. I don't really know how to answer this, so I'm not going to try. I'm sorry. Hopefully someone else can help.
3. Your teeth WILL loosen because that's what has to happen in order for them to move, so YES, that is TOTALLY normal. However, when you say 'grinding,' I'm wondering if you can elaborate more, because I don't want to tell you something is normal if it isn't.
Unfortunately, pain can be part of the process. I've read about some people who say they've experienced no pain at all, to others who experience quite a lot of pain. I'd have to say it's because everyone's experience is different based on their individual needs, but also because pain thresholds can be different. You and I could experience the same 'level' of pain, but it could FEEL more painful to me than to you or vice versa, just based on our thresholds.
However, if you feel a level of pain that worries you, don't hesitate to call your orthodontist because (s)he wants to make this as pain-free for you as possible. Only (s)he can tell you if what you're experiencing is 'the norm' or if something could be wrong.