Hi there,
A multivitamin is never a bad thing, you can add a b complex (water soluble) if you want.
If you're vit d deficient or your diet lacks vit d, then vit d is a good option, but it's fat soluble, meaning it can accumulate in your body- and the multi probably has 100%dv vitamin d..
Selenium is a trace mineral and (again) is probably 100%dv from a multi. You don't want anything over 400mcg from all sources or its toxic..