As I understand the new iTunesConnect philosophy :
- you can upload some multiple "eligible" builds to iTunesConnect int the "pre release" tab
- let some other testers test a specific build, via TestFlight (and declared as iTunesConnect users)
- when you come to a stable version, select the correct build version, from the "Versions" tab to submit to the AppStore, the usual way.
To me, you can have like 150 build for a pre release, it doesn't matter.