[I will not promote] Validating a German-hosted AI inference service before spending €60k

i will not promote. I’m considering a small B2B service that gives German businesses API access to open-weight models hosted in Germany, with clear retention controls and optional dedicated capacity. My early sketch assumes five to ten customers, but I have not bought hardware or signed customers. For founders who have sold infrastructure or technical services to small businesses, what did you do to validate demand before making a large capital purchase? Would you try to sell paid pilots using rented GPU capacity first? What customer evidence would you consider meaningful, such as a paid trial, a letter of intent, or a committed minimum monthly spend? I’d especially value advice on finding the first few customers beyond asking other founders whether the idea sounds good.