Sam Gerstenzang (@gerstenzang) and Dan Friedman (@dnfriedman) run what they call the "world's slowest startup incubator." Their model: Come up with a business idea, grind it to several million dollars in revenue themselves, then hand it off to a CEO to take it to the next level. They do this in industries Silicon Valley ignores. Their first company, Moxie, helps nurses open their own medical spas. It's now a Series C company with 600+ customers and a 200-person team. Their second is a funeral…