Sorry but I disagree on all the tetra's. Yes, they carry a lighter bio-load but if you take all 4 types your talking 32 fish. Plus they all have the same basic body shape. The tank will be crowded with little room for everyone to spread out and it will look visually "busy". Maybe that is what you want but you could easily do a combo of cardinals or rummy's, Lemon or diamond tetra's which are slightly larger with a different body shape, your DG, GBR, and cory's. This will give everyone their space without looking and being crowded. In the end it's your decision but it's best to err on the side of caution. You can always add something later if you want to.