I would like to use the free version on a site that I have in development, then upgrade it to the professional version when it is time for the site to go live. I wanted to ask if this is an easy process, or if it is better to just go with the pro version from the start.

Hello Jerry,

yes, it is very easy and painless. There is short FAQ on how to do it at:
How to migrate free to paid version without loosing existing URLs

Anyway, you can use the paid version of JoomSEF right away, as our licensing system allows you to enter two URLs on purchase - one for development website and one for production website.

Thank you jan, I honestly appreciate you taking the time to answer. :)