I'll address one point. Grandfather gave good advice.

3. -e vs -f. The documentation is not super clear about this. Basically a directory is also a "file", albeit a special one. The -e test will return true if the name is a directory or some other weirdo things that aren't relevant now. The -f test will return true if (a)the file exists AND (b)the file is a "plain file". Use the -f test. The -e test can return true for some things that aren't simple readable files.