Hi Julia,
1. Pothos is a pretty tough vine, I don't know if a Whites can smash it or not. It's very easy to propagate though, just put a leaf and stem in a jar of water and leave in a sunny spot so you could always have replacement vines ready.
2. Is it an existing background you want to modify, or build a new one? This link has a few waterfall setups:
Amphibian Care >> Waterfalls and Drip Walls in the Terrarium
I've never made one, but I'm planning a build like 2) in the above link (though 1) seems simpler), but with the waterfall made out of styrofoam covered in Quikrete. I've nearly finished a 13 gal. vivarium with a foam+Quikrete background (no waterfall) and I think it turned out well so I'm a Quikrete convert (pics to come in a week or so).
Here's a post by ViciousAlice that makes a dripwall/waterfall out of an existing foam backgound:
http://www.frogforum.net/vivarium-te...at-i-made.html
3. I just saw your post about the shipping of leaves from Josh's frogs to Canada. Wow! They may need a phytosanitary certificate to cross the border which would add to the cost and paperwork. Grrr, it seems so many things I find on the internet that I want just aren't readily available in Canada so I feel your pain. Anyways, I get my leaf litter from the bushes here, if you have an area you know is chemical free you could go collecting. Sphagnum moss seems like a popular option as well, but I've never used it.