A few ides for sight seeing follow. The Island is rich in things to see and do. Four days is really a short time. Buchart Gardens is a day itself for sure. The inner harbour area in Victoria is also easily a day. The comment regarding separating the towed is accurate. The ferry fee is based on overall length with the longer "units" being charged a premium. Just did the Blackball Ferry numbers. 303$ hooked and 269$ separated. My parents lived in Duncan.
http://findyourelement.ca/?gclid=CI-A8pOK4s4CFYQCaQodPTIPMQhttps://www.google.ca/#q=duncan+bc+totems Duncan totems
http://muraltown.com/ Chemainus murals
http://www.fairmont.com/empress-victoria/?cmpid=google_emp_search-branded-canada_empress-e-revsh&gclid=CMDI0Y-J4s4CFQYxaQodkq4BkQEmpress
Victoria
http://www.butchartgardens.com/