What risk with implementing NPSP3 directly to production?

This is my first ask, so hope it is appropriate question. It is recommended to implement to the sandbox first, but the sandbox would have no data, so to save time of setting up a sansbox with data, I want to go right to production. We are Enterprise Edition now with the standard Account/Contacts and some custom object. It very basis with only 3 active users now. There is a need for households, affiliations and slowly then donations,

I am seeking to understand the risk and what might happens to Accounts and Contacts when I implement it. Sorry that I have not dug into the documentation, but I am a volunteer and keep trying to make time for this.

I have a good technical understanding (certified Admin) but lack starter pack experience.