Your answer is close to perfect except for one thing - size doesn't necessarily have anything to do with spiciness (after all, what's bigger yet milder than a bell pepper, or even a mild Italian frying pepper?). There are many teeny tiny peppers that are TRULY hot enough to be painful. For first-time pepper users, something along the lines of a cayenne or the peppers you mentioned are a good bet though, and it always pays to keep in mind that it's much easier to add more peppers later than to un-spice a dish once they're in there. You can also adjust the spice by serving regular ground black pepper at the table; the combination of ground pepper and fresh chilies is a classic in Szechuan cuisine in particular because while they both produce the sensation of spiciness, the affect different areas of the tongue and complement each other.