We've just finished a huge project on a house. It wasn't a new build, but a complete renovation, doors, windows, floors, plastering, all kitchen, all bathrooms, entire plumbing and electrics. Big job. I loved it. Then I hated it. Then I loved it again. And so on.
We had my brother-in-law as architect, a good-ish contractor, decent builders, etc. But you still have to know that everything takes more time and more money than planned. Not massive amounts in our case, but still. If you are very tight on your original budget, then you will be in pain later.
WE had to be careful with protected restrictions on the property and licenses, etc from the loacl council always cause delays and expense.
But we're in.
And it's grand.