Seeking sage advice for starting a new project from ground zero

I am starting a new gig soon where we will be starting a new application from scratch and I would love some advice from experienced devs in the field. It appears I will be working as the only SWE alongside a senior architect and a senior database guy. There is a possibility of adding more devs. I have several years of SWE/dev experience but have never been at the very start as a lead, professionally-wise (I have tons of hobby and side projects that I attempt to hold to standard, but surely this will be different, right?). Does anyone have any advice they would be willing to share? Pitfalls to avoid, organizational patterns that were useful/not useful, tech debt practices that are sustainable?

I feel pretty confident in my technical abilities, and have seen a lot of good and bad practices over time. But being that I am laying groundwork for what could become a long-lived project, want to make sure what we put out is sustainable and reliable both technically and organizationally from inception to sustainment.