my advice in standard tuning is to either pick melodies with thumb carter style using key of c or g or use finger in style of john hurt again c and g and d are relatively easy.
i adapt carter syle by dropping the brush and repacing it with up finger on string above, by using strings 234, and using thumb melody on 5 string banjo, this will be the same as 5 string banjo in dgbd, you are two thirds of the way to being able. if you have a second guitar try open g tuning dgdgbd thiswill also help with 5 string banjo