1) Perhaps counter-intuitively, it's generally thought to be easier to enter a Snowball state when most of the continents are at the equator, the reasons being (A) silicate weathering of the continents consumes CO2 and is faster at low latitudes and (B) the albedo (reflectivity) contrast between ice and water is greater than the albedo contrast between ice and land. Ice is very reflective, water is not, and land is in between. In other words, if you grow sea ice at the poles, you make Earth more reflective, and the change in light (and heat) reflected per unit area of ice cover is greater for ice grown over oceans than ice grown over land. There is some background on the history of the Snowball Earth hypothesis, including the above points about albedo, here: https://en.wikipedia.org/wiki/Snowball_Earth
2) Definitely. I don't know the right answer yet, but here's a relatively recent (and relatively accessible) Scientific American article on the topic: https://www.scientificamerican.com/article/a-new-idea-on-how...