I am the sole person in my office. Is it still appropriate for me to use "we" when it is really just "me"? What is the thinking and rational behind this?

You can’t possibly deliver on the promise you made during Commitment to Hire™ by yourself. The “we” includes the Subject Matter Experts who comprise your Deliverables Team and are going to provide the actual advice to you about insurance, taxes, asset management, estate planning, etcetera. It will be these people who help you write the plan, or use the software to write the plan, and who make everything happen from account transfers to underwriting. This is why you use "we" instead of "me."