Starting a baking supply kit business. What are the first 3 things to focus on to get started?

Create a business plan. There is a LOT more to evaluate than what you mention.

Make sure that you use Shopify to make your online store. Best available. Would you be dropshipping them? Make sure you have a good ad too.

Start with finding your market. Assume as little as possible-your customer is not just like you. Remember 'build it and they will come' doesn't work. Learning your market intimately will help you with building traffic and hopefully with conversion. Once you have that; source suppliers, website (mobile first?) etc. If this is not a platform for home bakers you may want to focus on wholesale more than DTC

The most important thing is to find customers and confirm there is a market for what you're offering. You need to do that before all of the other items. Without that you don't have a business.

Agassi and Kurt are right. Although I slightly disagree with Agassi in terms of "'build it and they will come' doesn't work ". There definitely are instances where it actually does work. But they are comparatively rare.

Wasting suppliers time by going through a sourcing process that may never lead to anything is definitely quite low on the "how to win friends and influence others scale, and investing the costs and effort of designing, building and testing a good website without knowing pretty confidently that there's enough people/businesses that want to buy what you want to sell is nothing other than a good way to enrich the website development company. However, if you're still really keen on that, we do websites amongst other very valuable software and services.

To caveat the above slightly, it is fine to invest at the low end of moderate in a web presence as part of testing your market. But, the key there is to be circumspect. And wrt to Jack's suggestion of Shopify, yes it is an obvious good option (especially since it is a Canadian company and I'm in Canada!), but there are other options that are less expensive to start such as WordPress and Woo Commerce. Not as capable as Shopify, but you don't need wider/deeper capabilities until you do.

At least in my country - fully understand insane amount of burocray with regards to food saftey