Hi, Josh, and welcome to the BrickWood forum.
And let me say, I’m excited for you, and like many of the people here I understand why you might feel nervous. These are unfamiliar materials to most folks, even though our built environment is mostly masonry of one sort or another.
The good news is that, if you do the oven exactly per the directions, plus ask questions here (or search the forums first!), you’ll be in very, very good company. And…your idea to add stone or tile for decoration once the oven itself is built is exactly the approach we recommend.
Build a really good working oven first, then use tile or stone to add what we call a “veneer” layer. There are instructions for it in the oven build manual. And, you can check out this post to get your thinking process started. Again, search “veneer” on the forum to find all kinds of helpful advice and experience from other builders.
Please post back and tell us what oven design you’re building. Glad you’re here!