to decrease the overall bandwidth cost

You could increase the bitrate for partners at 15000
keep the same limit of bitrate for the affiliate at 8000

and for a new channel put it at 15000 for a limited time (in condition to have regular viewership and people talking in chat)

and having regular viewer being able to boost the channel popularity with channel points was also really good !

you also can reduce the maximum quality for new streamers to 720p 30fps
and unlock the vod feature only for affiliate and partners but propose to link a youtube account for the new users