The way I have seen is, the challenge is not creating the website or the sales workflow.
Biggest challenge is his you get people to trust your site.
You have to market it just right, which will cost a fortune. Then you have to make sure all your processes are in place (sales, basket, payment processing, returns, refunds, deliveries, Ts and C's, support, and customer service, data protection)
Then you have the job of making sure people can actually believe this is a legit website (1000s of these websites pop up every week which are expertly designed but they are scams, especially selling "discounted" high value items in fashion, kids toys, electronics etc)
So people are going to be quite doubtful until you have about 1000 plus feedback on various review sites not to mention your competitors who will do everything to make sure you don't come up or give you bad reviews by being "customers".
It's far easier to sell on someone else's platform if you have a few items to get rid of where you don't have any of these headaches and are protected in some way shape or form.
But if your goal is to get into the business and are aware that it is going to take you 8-10 years to actually begin to make it, then you ought to start now and keep at it.