Physical SIM cards

The SIM comes with the online order, it's a tri cut card with all 3 sizes in one package, so you push out the size that fits his phone, insert it, and the line goes active. You don't need to buy one ahead.

I'm not aware of a way to enter a SIM you bought separately during the online checkout, so picking one up at a store first wouldn't really save you anything. If you do grab one, make sure it's a postpaid SIM, prepaid and postpaid SIM cards aren't interchangeable.

If you'd rather not wait on the mail, doing the activation in a Koodo store is the faster route, the rep activates the SIM and starts the number transfer right there. Bring valid ID. Porting info here https://www.koodomobile.com/en/help/moving-your-number-koodo

If you only wanted to do it online, during the checkout option when purchasing a plan with Koodo or a device with a plan, you’re able to change it from eSIM to physical sim card. This can be done in the image below. When ordering, it now just defaults to eSIM but this can be changed.

After a few business days, you will receive an email saying that the sim card has been shipped. If you wanted to avoid the wait time of the sim card showing up, yes, you can purchase a postpaid Koodo sim card from a Koodo or Telus location and get going before the sim card arrives. However, you have to wait for that initial shipping email as once you receive it, the line is active for you to use and perform the sim card change.

Once you receive the “Sim card has been shipped” email and you have acquired a Koodo sim card from a store, you can simply replace the sim card in your Koodo self serve, switching the plan to the new sim that you acquired. You can do this by following the steps below. Note, the other sim card will still show up but will be unusable so just throw it away. You should also note that it would be much faster if you have a rep from a store set it up for you as there is now no longer in store activation fees and it can be done immediately. SIM card 101 | Koodo Mobile

To directly answer your question based on how I read it. 

 I dont recommend this.  Since purchasing/activating online and then swapping to the sim your purchased is a bit messy

Yes you will either need to order the physical sim along with the plan and it gets mailed. or you need to activate in person at a store or kiosk