Old saying:
a consultant is a guy who knows 1000 ways to make love but doesn't know any women
My current employment started out as consulting but it morphed into a multi-year design contract, so I basically became a self-employed contractor again.
You are obviously a subject matter expert but in the back of your head never forget LIABILITY.
It belongs to them, not you. Don't stick your neck out so far you end up owning the product or process.
You can tell them how they should do it but don't do it for them, unless they sign a contract
Good luck.