This is a general question with an Atahualpa part.

I'm planning to renovate our town's website and make it a Wordpress site. I'd like to use Atahualpa as the theme, naturally. Several town offices, like the clerk, building department, court, etc., will want to do their own site updating. Each office does NOT need its own look and feel, header image, etc.

I'm thinking I want to keep it fairly simple and not use WP Multisite for this, but just give each department secretary a username/password and contributor or editor status, rather than going all the way into Multisite.

What do you think? Which way would you go if you were designing this site?

I would go with what you are thinking Paula. Multsite just adds complexity where you don't need it IMHO.