There is no simple answer to this question. So much depends on what your product is, how unique it is, what the price point is, how mature the market is, how much competition there is in the market, how well know your brand is, how much you have to spend on advertising , how much money you'd like to make and how quickly you want to grow.
If for example your are selling something like enammel pin badges that is low cost, you are going to need to sell a lot to make your business worth while, even if you have one really nice design it is goint to be hard work because once a customer has purchased once they arn't going to have a reason to come back If you have a selection of pin badges then customers are more likely to find a product they are going to want to buy and there will be more of a reason for customers to come back and place orders with you agian. If on the other hand your products is say a specialist cake like a gluton free vegan xmas cake then your product is likely to be a higher price point, so you don't need to sell as many and as its a consumable product customers many place multiple order ber year, so a single product might be more feasible.
In the case of the company i work for, we have a physical store so we started with around 500 products, of several thousand lines we sell in the bricks and mortar store.