Cost of garden planning for difficult terrain

Hello. We want/need to start working in the garden soon. We bought a house from the 70s and first renovated everything inside. The outdoor area is just as old as the house and accordingly due for renovation. Unfortunately, our property slopes down by over three meters both to the back and to the side over a length of about 20 m. The problem, however, is that the house is built into this slope, and at the terrace, the garden at the highest point is 2.50 m higher. Difficult to describe... Unfortunately, we lack the imagination and ideas of how to design the whole thing nicely and sensibly, and we would like to have a professional handle it. What is the best way to proceed? Who does such things and where can you find someone who is good? The property is difficult and not a 0/8/15 towel. What costs should we expect for the planning? Has anyone had such garden planning done, and were you satisfied with the result?

Every plan stands or falls with your input. In the case of an existing property, the garden is already established and overgrown; what currently bothers you about it, and does everything really need to be redone?

Good evening, in order to develop ideas, pictures and (!) drawings would be helpful. Could you upload these for better understanding?
Best regards

A garden from the 70s often has too dense planting, often with cypresses that are too large and bare or brown at the bottom. But there are also gardens where you only need to prune the valuable shrubs and it looks chic again. The valuable thing about older gardens is that you now benefit from the use of trees that first need a few years, e.g. shade providers or privacy screens. We don't know how it is for you and why it is due now. I can only give the tip to first look at what exactly doesn't fit and whether anything can be improved in the structure at all. If you want to level a lot, it costs at the drop-offs. A new terrace and thinning out can almost be done by yourself. A garden architect is not cheap; a landscape gardener may also do.