Using the private use area in this font is absolutely the wrong thing to do. There's no need to use any Unicode points for the symbols, a font can have "ligatur

Using the private use area in this font is absolutely the wrong thing to do. There's no need to use any Unicode points for the symbols, a font can have "ligatures" (actually these are "glyph substitutions", via the GSUB table) which map to (non-encoded) glyph indexes, rather than mapping to (encoded) Unicode points. So defining a Unicode point for a ligature symbol is completely unnecessary, as there is an additional level of indirection which you don't explain in point 5.