Trying to figure how to continue my numbering for my "file 1:"

[j.crater]

imports are best placed on top of the file.
In line #9 you open file (only time in the code), and then in line #12 you close the file on every for iteration. Anyway, using context manager is a better to handle files. It will close the file automatically after you are done with the processing. Try something like this:

import os
import arcpy

def main():

    arcpy.env.workspace = "I:\\GEO5419_Python\\Lab2"
    path = r"I:\GEO5419_Python\Lab2"
    fcList = arcpy.ListFeatureClasses()
    with open(path + r'\listfeatures.txt', "w+") as file:
        for line in fcList:
            file.write("File 1:" + line)
            file.write("\n")  # writes next feature on seperate line

if __name__ == '__main__':
    main()