A few questions.

Hello teachers, I would like your help with a few questions please:

1. What is the main difference between "as for.." and "as to.."

2.what is the main difference between "I'm flying to Japan next week" and "I will fly to Japan next week" Except for the different tenses? I know one is in present progressive and the other is future simple, I just want to know more about the matter.

3. I've heard that I can't use past perfect simple without using past simple at first. Is that right? For example, would the sentence

"they are doing their best, and they had also won, prior to that." not be correct to use?

Thank you .