Sourdough starter questions

Try a mix of both. Are you using unbleached AP?? If it's bleached, it's worthless. I use King Arthur, can't go wrong with it.

Most of the what I've read and my personal experience suggests using a mix of flours to feed your starter and not just AP.

What's your proportions (and what re your specific ingredients) for feeding?

A few things:
—it is extremely common for an initial starter culture to appear superficially bubbly after a couple days of feeding, but it isn’t made bubbly by the yeast....it’s growing a culture of leuconostoc bacteria. The leuconostoc will crowd out the yeast, and you can feed it forever and it will never reach a sufficient yeast concentration to raise a loaf of bread.
—leuconostoc takes hold early on, before the culture is acidic (the sour of sourdough). Yeast reproduces just fine in an acidic culture, but the leuconostoc won’t survive the acidity.
—many people who struggle to get a new culture up and running find success by starting with an acidic mixture. Use a couple tablespoons of pineapple juice to mix your initial batch, and you will immediately have an environment that is favorable for yeast and not other wee beasties.

I didn’t make all of this up—a wonderful baker/microbiologist by the name of Deborah Wink figure it out when a volunteer group of hundreds of people from around the US were testing recipes for a Peter Reinhardt baking cookbook. Person after person, in various places around the country, experienced what you did: a superficially bubbly starter that fails to double or become really active. Her analysis of flour/water mixes and her microbiology training solved the mystery and provided a workaround. Google Deborah Wink and pineapple juice solution if you want to read more about her work. She can be found online from time to time at TheFreshLoaf.com, an awesome resource for bakers, whether newbie or seasoned.

Re: temp, yeast will be happiest in the same range as humans: about 68-78. Cooler, and things slow down dramatically. Hotter, and some off flavors can develop unless the culture is refreshed very frequently.