Nobody knows if 3d printed pla is non-toxic or not.

It's all down to long term exposure and currently there are no figures.
So far all the published studies have come down as ALL 3d printed materials not being entirely safe on a long term basis.
That said - for any length print most people aren't near the machines all the time.
But you can't categorically say they are 100% safe.

Printer wise, if you've got that kind of money the I'd go for something larger and better than a small printrbot.
And i certainly would not keep it in an active wood shop.
Bad enough seeing what happens to computers in such places, I'd hate to see the kind of crap that would build up on the motors, pulleys and screws somewhere like that.
But should be easy to build a perspex cage to keep them in and keep the dust out.

I agree that it's always better to have 2 or more. If going for a printrbot - and there's no reason why not, then go for the top of the range plus.

Build volume is fairly important and any large prints can be run over night.
That would leave you enough for a couple of wanhao duplicator 2.1 i3's as well and enough money to stock up on filament.
Or get a replicator clone for any dual prints. You could afford a creator pro and the printrbot plus.

I certainly wouldn't worry about enclosures, but then you might have to if it's a school, all those daft H&S regulations. One worth looking at is the cel robox. It's fully enclosed, has some very cool features and is fully certified for use in schools.
http://www.cel-robox.com/

And I think they're bringing out extra tool heads in the near futire as well. So has potential to be used as a laser engraver and maybe some small cnc stuff.