You'll need 60 DocCALs here. 10 of them to give your 10 users access to the "Selection QVW" and 5x10 more to give those 10 users access to the other 5 documents. You might consider a simple webpage instead of a QVW for the selection page.
HOWEVER! In this scenario you should not use DocCALs. As a rough guide, if a single user requires access to more than 3 different QVW files, it is more cost-effective to purchase Named User CALs rather than DocCALs. A Named User CAL will give a single user access to unlimited QVWs whereas a DocCAL only gives a single user access to ONE QVW.
Hope this helps,