Echo dot 2nd gen with Sonos play

When using the dot you will need to specify the room name/name of Sonos speaker even if you have a single speaker set up as otherwise the music will play from the dot. Also, in case you were expecting this, Alexa will only answer any questions via the dot - it does not 'speak' through the Sonos (unless you are using LineIn on a Play5 I believe)
As you only have a single speaker multiple streams will not affect you, but just in case you are thinking of adding to your Sonos system, you should also be aware that you can only initiate a single Spotify stream via voice, whereas you can start multiple streams from the app.
Any music playing will 'duck' ie lower volume when you speak to Alexa also - and if you have multiple dots this will happen regardless of what room that dot is in. e.g. if you are playing music on your single speaker and the kids are asking a dot upstairs, it will lower the volume in the lounge. It can be quite frustrating at times but we are learning to manage it! Sonos are apparently looking into this one to improve the 'ducking' feature.
Also I have noticed if I ask Alexa to increase the volume on the Sonos, that particular dot will keep that volume itself - so if I have cranked up the volume during the day, when I ask her to switch the lights off at night, she blares out 'OK'! Again, its a niggle and we are learning to manage it.
Despite the above, I prefer the dot + play1 set up to the Sonos One currently. I have returned the 3 Sonos Ones. The mics on the dot are much more responsive and doesn't false trigger all the time like the Ones were. Also you will get the 'full' Alexa features, some of which are not available currently on the One (messaging/drop in for example)
The set up is a lot more customizable on a dot as well e.g. can toggle wake sound on and off, can change wake word - you can't do this on a One.
Hope this helps