How to deal with left over work from a Post Doc
The easiest way to do this is to politely inform your previous advisor that you no longer have the time to commit to the projects you were working on as a post doc. It is not your responsibility to train others in his lab, or to take on duties beyond what you're comfortable with. 

One option to consider, if you're working on a "for hire" basis, is to offer the possibility of hiring you on a contract basis to do the work. You would then be able to set the scope and extent of the work, as well as your compensation. If your advisor was unwilling to accept the terms, it would put the refusal on him, and you'd be more or less "in the clear," so to speak. 

As for the pay rate, you should probably select a rate that is between the academic and corporate rates, but leaning more toward the former—remember that academic pockets are typically not as deep as corporate ones.