iPhone iCloud Backup vs iTunes Backup

[Boardiesboi]

Recently started backing up to iCloud and have a few queries

1. iCloud backup is only 6GB but I've used 35GB of storage on my iPhone itself. Does that mean if I restore using the iCloud backup, it'll have to redownload 29GB of stuff (eg. apps etc) using wifi?
2. I'm on iOS 11.1 Beta 2. Since iCloud backs up automatically each night, presumably the iCloud backup is only compatible with 11.1 B2 or later. Does that mean I cannot downgrade back to 11.0.3 using the iCloud backup?
3. You can archive an iTunes backup any time so you can have copies of your backup for different iOS versions. But there is no such option for an iCloud backup?

Thanks in advance.