The latest Echo Show 8 does not have the necessary audio out jack needed for it to connect to any Sonos input jacks.

Look for the older Show 8 or 5 that has this jack.

You don’t need to connect them by wire. You would use the echo show to wirelessly play music from, or issue commands to your five, once you set it up in the Alexa app. The echo should discover your five, and there’s also a Sonos skill. Not sure if the Sonos skill is even necessary now.  

but i should be able to connect the echo 8 and Sonos 5 via micro USB and 3.5mm jack, correct?

Only via 3.5mm, if you can find a socket at the rear of the Echo.

You should be able to connect the show 8 by 3.5mm jack, as long as your show 8 has the 3.5mm jack. I don’t believe there’s a way to connect via micro usb. 
 

From the internet:

1. Connect a 3.5-mm audio cable to the line-out port on the Echo.
2. Connect the other end of the audio cable to the line-in port on your Sonos. For a Play:5/Five, the cord should have single 3.5-mm connectors on both ends.
3. Open your Sonos app to enable Line In Autoplay under Room Settings.