Budget max. €700,000 There is no development plan. Desired living space approx. 130 sqm 3-family house possible (since the neighbor also recently converted 3 apartments)
If there is no development plan, it will probably be the case that you have to adapt the footprint to the neighboring buildings. This has nothing to do with the number of apartments. The footprint must fit the plot. You can roughly check this via Google Maps to see how the house relates to the neighboring buildings. That would almost be a doubling of the footprint according to your wishes. Another problem I see is that if you plan an extension, you have to energetically renovate the entire house at the same time. You are planning this, but it would be an enormous effort. It may be that €700,000 is enough for everything, but that is not done in a day; the project will probably take about a year or so. Ideas are difficult to make without photos, plans, or regulations.