Logistics of Shipping via Sea vs. Air

Hi all. I’m still in the research and product research phase and haven’t been able to find an answer to this.

If a supplier takes let’s say 3 weeks to prepare an order of 500 units and I ship by sea which takes several weeks to reach the US, what if I sell out sooner than I think – it would take at least 5 weeks to replenish the supply. Does that mean I should plan to ship via air at least until I figure out how quickly to reorder the product?