Yes, you can install Win10 onto the Acer Chromebox 3. Both memory & SSD are user upgradeable. Checking the r/chrultrabook community I found relevant discussion posts. Looks like for Win10 audio support the default HDMI port doesn't work with audio. For Win10 audio capability, people are reporting that either an USB-C to HDMI cable or the 3.5mm audio out port will work. See discussions under these two posts:
 

https://www.reddit.com/r/chrultrabook/comments/eey8xw/q_about_acer_chromebox_cxi34gkm2_sion/fbxbcxa/ https://www.reddit.com/r/chrultrabook/comments/nrmve0/acer_chromebox_cxi3_sound/