If I am supplementing with copper glycinate, zinc, vitamin C, MSM, calcium w/ vit D, omega 3 and a isotonic OPC antioxidant... is it really necessary to take a daily multi?
Also is it at all beneficial to take both a fish oil and flaxseed oil- or is one or the other good enough?

Yes, use a good multivitamin/multimineral. It need not be expensive.

Many relatively minor factors such as folic acid, selenium, chromium, etc. are needed.

Remember that the basic human nutrient needs are based on getting young rats to breed. But as we age, we are less and less like young rats.