Always use up to date and valid certificates, even within your own network.
If you have Blynk server running local, use a complex password and install fail2ban (if you are running linux). Use a firewall and don't forward any ports.
Furthermore, don't worry too much. There is too much sht out happening al ready without you ever knowing or realizing it. You should take a couple measures, like I indicated, but you can't go around being paranoid all day worrying someone will turn off your light or see how warm it is in your house