5 days on the Island would be good. Lots of options but you could do something like:
Day1: catch an early ferry over to Nanaimo and ride Doumont or South Nanaimo area. Nanaimo trails are fast and flowy with plentiful quality loops. After riding all day you could overnight and grab a bite.
Nanaimo Map
Day2: Head up to Cumberland, grab a map from Dodge City Cycles, and ride. Check into Riding Fool. Eat and be merry at Waverly Pub.
Day3: Get up early and head to Hornby. If you're feeling cheap and pedally you can park your car at Buckley Bay, catch boat over to Denman, pedal across Denman, catch boat to Hornby, and enjoy singletrack. Overnight Riding Fool.
Day4: Drive up to Campbell River and enjoy some Snowden singletrack. Overnight Riding Fool.
Day5: Ride Forbidden Plateau or Hammerfest then drive home tired and happy.