If you've solved all these problems yourself at your org: congrats, you re-implemented Tailscale with a bespoke solution that takes orders of magnitudes more $ to maintain and audit regularly than just buying an industry trusted solution.
Tailscale is, all things concerned, really cheap. It costs less at my large org than a single engineer. Doing it ourselves would take a team. Maybe two. Once again, HM primarily comments from a naive engineer's perspective, not from a leadership view.