No. In fact, it is advised that the applicant should not purchase any tickets that can not be refunded before the interview. He may make reservations but there is no need to show that you made trip arrangements. What is more imoprtant is him showing strong ties to his country.
His B2 application will have nothing to do with you. No point in even thinking about this.
He should still bring supporting documents of his strong ties with him. Even if they don't ask for them he should be fully prepared.
Should not be an issue. As long as he has continuous work in house country..
Once again, his application has nothing to do with you. He is applying on his own merits.
It is better if he can show that he can fund this trip himself. And he should definitely provide financial evidence on him being capable of doing so. The less other people are involved with his application the better. Remember, he is applying under his own merit. With that said, he can certainly have someone else helping or funding the trip. It will not be as strong a case as if he was doing it himself, but it will also not be deal breaker.