3. Not at all. The halacha differentiates between charity and business loans.
4. You keep trying to put the chainek back up. if the new guy lives in the city or at least pays taxes and does not block the way to the existing store, and certainly if he sells specialty pizzas, it is muttar. While there are some restrictions are simply protections of proprietary rights. See Hasagat Gevul: Economic Competition in Jewish Law by Rabbi Chaim Jachter (on-line).