icloud drive on 2 iphones , ipad and a windows 8 PC

I have been asked to upgrade 2 iphones, ipad to IOS 8 - which is the subject of a different thread here

The user then wants to take advantage of icloud drive - and will pay for the storage

will icloud drive just work like dropbox/one drive - in that
1) it will act like icloud and keep a full backup
2) It will just act like a drive - so he can copy all photos, notes etc across to the drive and be available on any other device
3) Will all devices need to be on the same appleID to access the icloud drive ?

just generally how good is icloud drive now - ?

My second set of quesitions - are around updating the 2 iphones and ipad from IOS 7 to IOS 8
I will do an icloud and itunes backup - BUT it would be good to be able to separately make sure the email , photos etc are also copied onto the PC - so I can actually see the items are copied and know i can get all the data back

I played with an iphone 8 today and it did not appear to be that easy to do - any suggestions welcome
thanks

Once they are updated to IOS8 , i will then use the icloud drive - as per the questions above

thanks

Please do not double post. Your duplicate post has been removed.

I thought it was better to have two posts as the subjects I thought were diifferent
one , this one was about using icloud drive after performing an ios8 update
the other post was about the process of actually doing the update from IOS7 to IOS8 and backing up etc
so sorry for misunderstanding the rules , i just thought as they are two different subjects - i should post separately.

I will edit my post here to also include the questions about upgrading - thanks