Working the original question first..
If Team A touches the ball before it goes 15 yards as cowman said, it is a violation that gives Team B the option of taking the ball at the spot of illegal touching.
So, Team A kicks off ball goes 5 yards and A15 picks up the ball at the A35, it would be Team B’s ball at the A35, 1/15. It is not a foul and there is no penalty involved. In fact, if there is an accepted penalty, then the spot of illegal touching goes away. Same as before but the ball goes out of bounds at the B38 after A15 touched the ball without being touched by Team B.. in this case the kick out of bounds would be declined and B would have the ball at the spot of illegal touching as that spot is more advantageous to the receivers than the enforcement of the penalty. If say the ball went OOB at the A36, then the penalty for kick out of bounds would be enforced and B would have the ball 1/15@A31. So you can see there is a difference.
Second question, Team B can come out and initiate a block against the kickers with no penalty, if they do actively come out to block, they lose their protection from the rule quoted above and Team A should not be flagged for engaging a Team B player that initiates contact... however if the Team B player comes out to recover the ball and is not engaging in blocking then he is protected from being blocked until the ball has traveled 15 yards and touches something.
It is a very tough call at times and that is why in NCAA it is reviewable for the touching and recovery of the ball as well as early blocking and is one of the few fouls that IR can “create”.