Welcome! Airlock activity only gauges the release of pressure. It is common for that to stop after a could days - or on occasion continue for several weeks. Your batch can continue despite the lack of airlock activity. The use of secondary vs. primary-only has merits on both sides. Many, including myself, typically do an extended primary-only fermentation, and only use a secondary when adding adjuncts (such as fruit, coffee, vanilla, etc.) or if you are aging for an extended period of time. Some of the benefits are that it's less overall effort, and because it's one less transfer it carries less risk of contamination and oxidation. When you get a chance I recommend researching the opinions and experiences of both sides of the equation.
Again, welcome to the obsession, and good luck on your stout!