You do not have to be a resident of Nicaragua to purchase property or to operate a business. Many of the expats living in Nicaragua have chosen not to become residents. They simply must renew their visa every 90 days by leaving the country for three days or getting a three month extension. Becoming a resident does not affect your nationality i.e. you still retain your passport and the rights of your country of origin.
Having said that, there are advantages to becoming a resident of Nicaragua. Most Nica banks require you to become a resident to open an account and you may have difficulty without it to buy a phone and set up the payment account.