If I have high ACT and SAT scores, and a strong college GPA, what are my chances of getting into Tisch (NYU)?

I think your chances are slim with a GED and only one semester of college-level work. NYU will want to see proof that you're capable of more than one semester of achievement. If you attend community college for a year and half and do well in your classes, you'll have a better chance of getting in. But Tisch is a highly sought-after program and you'll be competing against highly motivated and experienced students from around the country. So aim for Tisch, but do some research between now and then and identify some other schools that you'd be willing to consider. You might also see if there are local theater groups in your area that offer courses or that put on plays that you can be involved with.