We are setting up a financial power of attorney for my mother, naming me as the agent. Can I be paid an hourly sum for my services, and can I participate in financial transactions that I conduct on my mother's behalf?
You are quite right to separate your two questions. Whether you can be paid for your time and efforts is an entirely separate matter from whether you may benefit from transactions you conduct for your mom.
In the power of attorney document, your mother can specify that you should receive an hourly fee for any work you do that is authorized by the document. Then, for example, if you spend eight hours working on her taxes, you may draw from her assets to pay yourself according to the arrangement set out in the document.
The document may also allow you to benefit personally from transactions you conduct for your mom. This means you may, for example, arrange to sell her car for her and then buy it yourself -- for a price that's fair to her.
If the power of attorney doesn't specifically permit you to benefit from transactions -- and many do not -- be careful when you act. You can pay yourself according to the terms of the document (keeping careful track of your hours and wages), but you must avoid all other actions in your role as agent that may benefit you personally.