Yes it means that you have prepared yourself for what you need to do.

"I'm all ready" and "I'm all prepared" are the same as "I'm ready" and "I'm prepared". 'all' my be used to emphasize that you are ready though. If you are not 'all ready' then you can not be 'ready', but you may be 'almost ready' or 'not ready'.

Yes.

right. they both r the same. if u're ready, ofcourse u're prepared for something. so there is no difference. Dad: "are you ready yet?" Mom: "yeah. I'm all ready. Let's go" I'm all prepared also can be used when u had to make arrangements for something. for example a party and ur friends would ask if u have arranged everything already. U may say "yeah. I'm all prepared for the party tonight"