Hi @dbblackdiamond -
I wanted to read through everything but seems you have receive a lot of very good advice from @ScruffR, @AndyW and plenty other people on your post.
Just a complete newbie’s two cents worth - Have a look at Reed relays. I have managed to use them successfully with Photon, Xenon and Argon without any difficulties. Specially if you switch lower voltages and current. Having said that, you can switch top to 3A with some of these relays and some even include a diode. They are small and can be used easily on breadboard while prototyping or mounting on PCB or DILs. See image attached from DigiKey… note the coil voltage and current requirements. Can work with 3.3V and and as little as 5mA.
They made life a lot easier for me, hope this can help. Please note, I am quite new to all of this, so please double check and make sure it is suitable for your application 
Anyone please feel free to correct if I made any wrong assumptions!
Regards!