There is an new trail map for Cumberland. It can be bought for a small fee at Dodge City Cycles. Pretty sure it's online as well. The guys at DCC can help you with the riding trails you want. 10 kms up to the top of Switchback for 1.5 hours of down.
Maybe plan a bit of Snowden Demonstration Forest instead of Forbidden Plateau just in case. Riding wants and needs may put Snowden in Campbell River in your sights instead of Forbidden.
Do not forget Dumont Trails in Naniamo as well. Fantastic stuff much like Cumberland and Snowden.
http://cvmtb.com/index.php/trails-maps/comox-valley-trails/ has a lot of maps and
areas on it.
If you want a route in Snowden I can offer one.
Hey, welcome to the Island, enjoy.