I guess it all depends on how complicated the project is, how difficult the site is, how experienced the contractors are, and a bunch of other things that just aren't coming to mind right now. Just start by talking through the project. I do think you need one. If you're still looking for a company, I recommend
https://oakshs.ca/deck-builders/. In my case the project itself was pretty simple, but the materials we chose weren't available, so we actually spent more time waiting for them to come in than building the deck.