There but for the Grace of God go all of us. Sleepless nights included. The forum has been invaluable for me.
Try to visualise things going well. If nothing else, you’ll feel better.
Other thoughts, could you reduce your plans, to have a smaller, more basic house to house your family and extend later? (You can’t claim the VAT back on that bit tho’, there’s always something…)
Or if you are renting, move into a static on site to save money? Lots of advice about this on the forum.