First, don't buy a rating, leave that to the owner. You cannot possibly know which rating will be required for the job you want.
Second, part time cintracting maybe difficult without time in type. No one with a $50 million jet wants you to be a student on it.
Third, do you have any corporate experience dealing with owners and their passengers--likely needed. It isn't a lark as your comment, "thinking about joining the scene" would imply.
If you're outside the US, disregard, foreign owners don't seem to care who glides them.
GF