Nice you can find joy in the project.
It will be Aluminium, Metal Core PCB (MCPCB).
All 3535 are Samsung LH351H, the pad designs are in the data sheets in post #31, (lh351h_red_rev1-2_8-20-18-pdf, page 8 e.g.).
I don't know whether we mean the same with "ground", I still have to figure out a...