...
The upgrade process is super easy, I was pleasantly surprised, but then you have to deal with your households. Go here https://powerofus.force.com/articles/Resource/NPSP-Convert-an-Existing-Account-Model-to-the-Household-Account-Model and if you are not freaked out by checking ALL those boxes before you start, then stop what you are doing and understand it first - this is a big deal.
I would then rename or remove the Household object, and remove all the Household reports from the Report Types list.