I always install all apps (except for maybe matching gifts) because there are too many linked things that could go wrong if they are not all installed.
See Accounts for setting up your Accounts object.
See Contacts for setting up your Contacts object. Optionally rename Contacts to be Individuals depending on the balance of individuals in your data mix.
https://powerofus.force.com/articles/Resource/NPSP-What-is-an-Account-Model
I prefer the 1x1 account Model.
Advantages
Disadvantages
Affiliations works well and is a great feature of NPSP although the new feature in Salesforce of one contact to many accounts also works well.
Households with the NPSP 3 is much easier to use.
Why does Matching Gifts install a Donation object when NPSP renames Opps to Donations?
Depending on the type of money you receive, think about renaming Opportunities to Donations or even Money or Payments.
Entering donations - read http://nickhbailey.wordpress.com/2012/04/09/how-do-i-enter-this-donation-a-primer-for-npsp-users/ especially the picture. (Quotes below from this article).
The person making the donation is added as the Contact Role.
"The Primary Contact Role determines which Contact will get this Donation rolled up to their giving totals. This would be desired in almost every individual giver scenario."
Remember:
Think about using Opportunity Primary Contact validation to ensure all Opps have a Primary Contact.
Understand Soft Credits!
Rollup Setting is in the Household Settings tab.
http://training.handsonconnect.org/m/6676/l/75076-how-do-rollups-work-in-the-npsp
This is a very good answer on Stack Exchange http://salesforce.stackexchange.com/questions/8392/donation-roll-ups-are-not-working-on-contact-and-household
Remember: