Nick here from Shopify, great questions!
Shopify has a 14 day free trial for exactly this. You can build out a website/ store and see if it's a fit for what you want and need. The trial begins when you start your store and you won't lose any progress or work once you purchase a plan, it will be the exact same but be ready for you to go live when you're ready! You can read more about the free trial here. Something to note is that you won't be able to sell any products while on the free trial, but if you decide before the trial is up you want purchase a plan you can do so to go live and start selling.
You can also see the different plans and pricing for Shopify here to give you an idea of what you might want to get if you decide to go that route during the trial.
Hope that helps and don't hesitate to ask any other questions about Shopify or setting up a store in the meantime.