You can go for the same architecture Odoo started using when they needed scaling. There is a talk in the Odoo channel that  can help you solve your issue: https://youtu.be/A_BWyFeGgVA

Long story short: for separation you can replicate your server one-way on a web available server, and keep the business functions on a central server. Web can be balanced and replicated independently, according to your needs.

You can always do as you mentioned and ban certain URLs and methods through the reverse proxy, completely disabling whatever you feel is delicate information (ie, the @/web/database/manager url).

As for what is better suited to your case, it will depend on the traffic volume you get, but I would suggest starting with option 3. Just monitor it's performance, set up alerts on the right metrics and avoid making your infrastructure more complex until you really need it. Make sure the workers are set up correctly and backup regularly.

Good luck!