first you need to contact your suppliers and companies to work with you on shipment. Know what to see, what people what etc. (you can't be selling designer shit in the fall thinking it's going to sell the same as the summer.) Know the market (genre) that you're selling to and the quality.
Ebay is pretty general about everything so it's not required that you have your own dropship site since all they generally care is where the package is from, when and where to send the package but it does make the customers trust you more, makes you look more professional and reliable to buy from.
Ebay fees are around 10% but that is fine tbh, just mark it up to how much profit you want ie: if your selling the item for $200, ebay is going to take $20 and the manufacturer is prob gonna take $150 which leaves you only 30 so mark that shit up to like 220 and ur good.
There isn't really much besides that since everything is straight forward