Gosh, I think the biggest hurdle to starting in to wet plate is all the different places you need to order the stuff from in order to start shooting. I'll try to run down the list -

Chemistry:

www.artcraftchemicals.com (silver nitrate, cadmium bromide, ferrous sulfate, ammonium iodide, Gum Sandarac)

AND

www.chemsavers.com (ethyl ether and glacial acetic acid)

AND

www.mavidon.com (collodion)

...

TheFlyingCamera