I made Peter's Potato, Cheddar, and Chive Torpedoes today from BBA. If you haven't tried this recipe, you owe it to yourself! Man, these are good!!
Sorry to hear about your starter's puzzling behavior. My impression, from what you have said and what you have left unsaid, is that you are trying to begin a new starter, following gaaarp's tutorial. If so, you've made a good pick, since gaaarp has done a thorough job of stepping you through the process.
Regarding your first question: the lively activity you saw in the first 2 or 3 days was bacterial, not yeast-driven. As a matter of fact, the yeast in your starter hasn't really woken up yet. It will start to thrive as the pH continues to drop, complements of the many generations of bacteria who are living in your starter now and producing various acids. That is why gaaarp has been so emphatic in his Day 4 discussion about the importance of waiting and being patient. Sometimes, that is all you can do with a nascent starter: wait.
So, following gaaarp's instructions, since you have waited more than 48 hours without any sign of doubling, go ahead and feed it some rye flour and some water. Then wait some more; a day or two if necessary. As gaaarp notes, it will eventually double and you can then proceed with the Day 4 feedings.
Hang in there. If patience is one of those virtues you have pursued unsuccessfully, sourdough will give you plenty of opportunity to develop it.
One other thought: what kind of temperature are you maintaining? Most starter activity tails off dramatically if the temperature goes below 70ºF. That's true of baby starters like yours and old timers that have been around for generations. If you can provide your starter with temperatures in the mid-70s to mid-80s range, it will be a happy camper.
Best of luck.
This is one of my favorite recipes! Delicious...