Not convinced that some of these questions are all that helpful, unless you know how to interpret the answers. For example:
"Q5: What are your fees?"
If he tells you the answer to this question, how would you decide from this information whether he is "an experienced, trustworthy tax accountant"?
At best it will tell you whether he is "a competitive accountant". If he is very experienced, then his charges will be higher than a less experienced accountant. Perhaps a high chargeout rate is a positive indicator here?
"Q9: Do you think I am overpaying/underpaying etc tax"?
This question could be interpreted in two different ways:
"Q9A: For my current circumstances am I calculating the correct tax liability?"
or
"Q9B: Is there some way that I can rearrange my affairs so that my legitimate liability can be reduced?"
There are not subtle distinctions between these two that are wrapped up in your single Q9, but they need to be asked and answered separately for any meaningful conclusion.
To my mind an important omission from the list is personal recommendations from existing clients who are known to you and whose opinion you value.