In the following song, it seems like the lead instrument is some sort of vocal or something. What would be a good way of replicating that sort of song using a synth or sampler etc? The lead enters at around 0:24.
I think it's a granular synth/sampler on the chipmunked voice. Watch this and you'll kinda get an idea of what they can do to vocals.
This sounds like a vocoder, maybe a vocoder with a sidechain (I'm talking as a happy user of Logic X, so I don't know what is possible in other software).
I just did this with a "singing" version of your first sentence:
See a really good howto here: