Live Ball Substitution

[stripes1977]

Here's a few questions that I would likely be able to answer fairly quickly if I had my rulebooks with me today:

A substitute enters the field during the down (assume that we only had 10 players on the field and the 11th enters the field after the snap). This is a live ball substitution infraction, correct?

What is the enforcement spot for this foul and what are the rule references?

For illegal participation (live ball), we use the All-But-One enforcement preocedure as usual, right? Is this the case with a live ball substitution penalty or is this treated as a non-player foul?

The plays that are in my head are:

Team A player steps out of bounds and returns. (Illegal Participation) ENFORCEMENT SPOT?

Team A (12th man) player runs off the field through his end zone (or wrong sideline) just after the snap. ENFORCEMENT SPOT?