I have no clue about metal clays and their toxicity, but if you're thinking about ventilation....you're not alone.
Actually, I'm thinking of getting the smallest of these
http://www.ventafume.com/content/pages/place-a-ventModel FE-500.
The biggest draw for me, is that I can solder in my home studio in the winter with the windows shut, by venting it through the wall. [I'm in Toronto, Canada and winter is long...especially THIS winter.]
It's not the cheapest solution, but I love that it's not real loud.....and it comes as a kit.
When I've added up all the bits of things to do this myself.....I didn't really save money and the fans were always REALLY LOUD.
The only other one I've seen, which is 'cheap-n-cheerful', but only works if you live in a warmer climate and can open windows.
http://www.onlinejewelryacademy.com/ventilation-video.html It's from the Online Jewelry Academy and the fellow shows
exactly how to build it.
Good luck,