Since the iPhone 14 series still uses a lightning port, you can use your old chargers -- they just won't charge at the maximum rate. There's nothing wrong with this, and it's arguably ever-so-slightly better for the battery. Fast charging can generate heat, and heat degrades the battery faster. Using the old chargers generates less heat. However, whether or not this makes a big difference in the long run is arguable (I'd argue that letting the battery percentage go below 20% has a bigger effect upon battery longevity).

To answer your question about chargers: any quality charger should be good. In the case of USB C, you need a 20W or larger charger but, since you have a PM, anything above 30W is wasted unless you also have something like a Macbook that can also use it.