Self-employed

Do you mean your industry code? You can look up your industry code on the Stats Can website: North American Industry Classification System (NAICS) Canada 2022 Version 1.0 Or you can use the search tools on the NAICS website: NAICS & SIC Identification Tools It doesn't have to be exactly what you do, it just has to be close. 

Your fiscal year can be Jan 1 to Dec 31, and you don't need to mark that it's your final year if you are going to do the same work next year.

Box 28 is also self-employment income if it consists of fees collected for services you provided. But even if it wasn't the CRA will likely just move the amount back to the right box because that's what their copy of your T4A slip shows.