Technically anything from 80% wireless usage and below is 'acceptable'. It just means your getting your monies worth is all, so nothing wrong with letting the AP do its job 😃
If a device is doing active file transfers etc. across the radio, then it seem only normal that the utilization would go up.
The non-802.11 interference is the stuff I worry about because it can usually be mitigated if you can track it down and remove it. Sometimes you can't though, and other 802.11 networks there isn't a thing you can do. Except maybe to talk to your competing network admins and work together to ensure nobody is using channels other than 1/6/11 and introducing ACI.
Your best bet is to get off 2.4GHz if you can, or at least have unique SSID's for each band so that you don't have to rely on band-steering not working 100% (because it won't).