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There are a few common issues that can cause this. You can read more here: https://openvpn.net/index.php/open-source/faq/79-client/253-tls-error-tls-key-negotiation-failed-to-occur-within-60-seconds-check-your-network-connectivity.html
Then you would have to make the Pi your main router and have configurations for what traffic should go where. It can be done but is a much more complex setup that I wouldn't do for two reasons.1. It will take a lot of maintenance and testing to make sure you don't have a DNS leak or similar that will expose your traffic.2. Depending on your internet connection the Pi isn't powerful enough to give you all the speed.
Are you sure that the printer is setup with the correct IP when you added it to windows? It might get another IP over the VPN. Try to add it again over the VPN.
Just give it a fixed IP address in the same subnet and it should work just fine. A more "sexy" approach would be to add a DHCP server to the Pi but that would require some more work.
Hi, haven't had any issues so far. Not a daily user my self to be honest. Every now and then the outgoing IP's get blocked but they usually sort it out fairly quickly.
Were are you stuck?
It might be that the android doesn't accept changes to the settings supplied by the DHCP. Try changing the config that the DHCP assigns to the clients.
If your router doesn't allow you to set specifics then you have to use a secondary DHCP.