Thanks for your contribution -- as usual, my situation is a bit more complicated.

I have a master configuration file with a list of sites. Each entry has a name, whether they're enabled, and the name of the file that contains that last order number. From the name (Foo, in my original post), I'm able to find the module with the credentials. And, although I wasn't crazy about the idea, a database is starting to make sense (especially for the last order number), but I really like the low maintenance feel of just editing a text file, compared to fiddling with a database.