Sounds all good at first. We also built with a general contractor, and I would always do it that way again, provided it’s a good general contractor. It at least takes some work off your hands; after all, you still have to manage everyday life and work during the construction phase.
However, I would only sign after the planning, and this should definitely be included in the contract with the floor plan. Make sure that a fixed price is agreed upon. Otherwise, the process was identical for us.
I find the note from important: if both of you are repaying the house and taking out the loan together, you should both be listed on the land register. Since she is bringing the land, you might need to think about that. Maybe you have the equity? Even if everything is fine now, no one knows what things will look like in 10 or 20 years. Separations can get tricky, which I certainly don’t wish for you. Then you might end up empty-handed, and she has a house you paid off 50% of for half your life. And it doesn’t stop there—the loan must still be paid. The bank doesn’t care what happens in your private life.