I guess that I had not researched those strips enough. 60 LED/m seems like it could fit our design goals, if I were to get these strips, what would be the easiest interface to allow for communication between the strips and an arduino?
One Arduino pin can drive millions of them. Just connect a wire to the first LED in the string.
Another thing that deterred us from using the strips is that since we might be making some sort of LED-covered animal, there would be many edges where having strips could be problematic. For these areas, what would be the best way of controlling many LEDs?
You can cut those strips into pieces with scissors between the brown dots.
(the "brown dots" are solder pads for attaching wires to the freshly-cut ends...)
Would using an I/O expander work with these?
One piece of wire is all you need, that's the whole point of the WS2811.