My answer to this depends on what you mean by "professional philosophers who think about". You have to be aware that subfields have selection biases. For example, the percent of philosophers of religion who think God exists is much, much larger than the percent of professional philosophers generally who think God exists. This is because if God does not exist philosophy of religion ceases to be a productive area of research. Conversely, if you have an irrational attachment to the idea that God exists this than you are likely to spend an inordinate amount of time trying to prove one exists. This issue is particularly bad with regard to religion but it is in some sense generalizable to all or most other subfields. Philosophy is also a competitive enterprise and there are various incentives to publishing novel arguments. This means in any given subfield views that are unpopular among philosophers generally will be overrepresented.

So the circle you draw around "professional philosophers who think about [subfield x] questions" needs to be small enough to target experts but large enough that you don't limit your survey to those philosophers who are very likely to hold a view you are surveying in virtue of the area they work in. I think the right circle is something like 'professional philosophers who are equipped to teach an advanced undergraduate course in the subject'.

Edit: The free will question will depend on what you want out of a conception of free will. But the understanding of free will that most lay people have is totally impossible.