When should a dropshipper start holding their own stock?

As soon as a line sells consistently for two months. That is the point where the margin gained from holding it usually pays for the storage inside a single turn of stock.

Why the answer is what it is

Do it per product, never all at once. The capital needed is small because you already know the line sells, and the two things you gain — margin and delivery speed — are the two things that decide whether there is a second order.

What this looks like in practice

A dropshipper who survives past the first year almost always stops dropshipping — they start holding stock for their best sellers, because that is where the margin is.

Returns are where the model is tested. If your supplier will not take a return, you are the returns department.

Dropshipping’s hard part was never finding a product — it is that you do not control delivery, and delivery is what a customer remembers.

Where a mobile app comes into it

An app is worth building once people buy from you a second time. Most dropshipping stores never reach that point, which is why the honest answer here is usually ‘not yet’.