Thanks you two for your help. I really appreciate it.I'm working quite a bit of paper mache right now, and my basic recipe is either thinned out white glue OR thinned out white glue with some flour in. I don't measure.
Then I am using home made paper clay to make nice, smooth finished surfaces.
Here's a tutorial on making paper mache armor, that contains the details of the paper clay:
The Gourmet Paper Mache guy has some interesting techniques too: http://papermacheblog.com/
Glue-All is supposed to be better than school glue for mache, because school glue continues to be water soluble after it's dry. But glue-all is harder to find, at least around here. I've used both without issue. Mold isn't something I'd worry about in a finished piece - if the mache is applied thinly, one layer at a time, and allowed to dry then it will be dry and there won't be enough moisture for mold to form. Mouse or insect damage during storage might be more likely.
Ever noticed how fast a loaf of sourdough bread dries out and gets hard? Same kind of thing with the flour pastes, I think.
Something like wheat paste, used for applying wallpaper, is another option. There's a lot of ways to do paper mache, and it's mostly just finding what works for you.
A common problem with using flour is bugs and rodents eating your hard-built props during the off season when they are in storage. I would hate to put all that work into something and then pull it out next year to find almost nothing left.