Set the budget and add 10 % for unexpected expenses. If you absolutely need to, you can alter the budget later but this will provide you with a good guide line.
Leaving one wall open without cupboards makes the room interesting and inviting. It is monotonous to have a wall-to-wall and floor-to-ceiling room full of cabinets.
Your kitchen is not a showroom so don’t try to make it look like a showroom. The design should be inspired by your family’s lifestyle.