I don't plan to go to Japan, but if I did, I'd still like to connect to MINIBOT with my phone and see what's going on under my couch.

I already use Tailscale, so I will install Tailscale on the raspberry pi in order to access it from anywhere. I set up a second wifi router with a different subnet than my main router. The pi is connected to internet through wifi, and to the second router by ethernet. Now I can have MINIBOT and whatever other wifi sensors I want to talk to the Pi able to do so but not take up traffic on main router or be exposed to the main LAN. 

(WWW)---(home router)
             |
            wifi
             |
         <TailScale>
        [Raspberry Pi]
              |
             eth
              |
          (router2)
         /    |    \
        /     |     \
     wifi    wifi   wifi
      /       |       \
 [minibot]    |        \
( OO( )( )   [?]      [?]