How many minimum validators are needed to run a substrate solochain? Is single validator enough to run a Substrate solochain, if we are not parachain?
It depends what kind of solochain you are making, for a system to be known as a network there should at least be 3 nodes and all should be validators. If you want to make a network with only a single validator than I would say it is not a blockchain as all the power of the network is in hands of a single validator, that is the property of a centralized system. As for your question you can run a solochain with single validator and also there is no minimum validators required to run a solochain.