This is a topic that I find quite hard to cover because I am approaching this project with professional experience. I never doubted that what I was doing was not the right thing. If you do have doubts, stop. I am a relatively organized person, so many decisions had been made before starting on site. I also recognize that once on site, the design thinking and decisions were made and that any changes needed to be mindful of this to still work with the overall result. These aspects may have helped, as there were plenty of decisions to make throughout the process and I can see how this would be overwhelming for some. Maybe being in the industry made understanding how things worked a little easier, although I suspect that some tradies may disagree! A little knowledge can be a dangerous thing! I do have trust in the people who worked on my project. This made a huge difference. Mistakes can be fixed and all projects have challenges.
I made an effort to meet them personally, learn something from them and also tell them when they did the job well. The one thing that did seriously test me was the lack of sleep and exhaustion from an increase in "stuff to do". This did contribute quite a lot to the few moments that I did feel overwhelmed.
I think the advice I would give to pre-project me is, "Sometimes things don't pan out the way that you thought they would, but it is going to be pretty darn good, you are doing great so get some sleep!"