A: Around 100$ then it will grow.
B: Games / Consoles because you can buy them for cheap @ sales and some discount sites.
C: I would sell each item for the average selling price, but buy it for cheaper, so a PS4 which usually costs lets say 200$ and I bought if for 150$ I would sell for 200$.
D: It is reselling and making a bigger profit, as I earn more money I can invest into more items and resell them.