I can confirm you can install/setup an Echo device without an Android or Apple device.
I did so long time ago and I only had PCs and Windows Phones at the time (there is no Alexa app on WP).
It's one thing I like about Amazon compared to Google : in order to set up/configure a Google Home, you HAVE to own an Android/Apple smartphone/tablet otherwise you're screwed!
Google does not provide a website like Amazon does with
https://alexa.amazon.comFor some features on the Echo, you do need the app on an Android/Apple device though (calls, routines, etc...).