By using high-resolution spatially-resolved laser-based angle-resolved photoemission spectroscopy, we investigated the intrinsic electronic structures of the CuO₂ planes in multilayer Bi-based cuprates Bi₂Sr₂Ca_n−1Cu_nO_2n+4+d (n=5~8). The inner CuO₂ planes are well shielded from the disorders in these multilayer cuprates that provide an ideal platform to probe the intrinsic electronic phase diagram. We observed well-defined Fermi pockets with a hole doping level as low as 0.007, demonstrating an abrupt transition from the parent Mott insulator to a metallic state upon the introduction of a tiny amount of doping. We identified a cuprate system that consists exclusively of hole Fermi pockets. It challenges the conventional understanding on the role of the nodal and antinodal electronic states in driving high temperature superconductivity. The observed Fermi pockets exhibit unusual layer-, momentum-, temperature- and Fermi surface-dependent energy gaps. Substantial electron pairing is observed along a Fermi pocket with an energy gap up to ~42meV in lightly-doped CuO₂ planes (p~0.05). These findings indicate that high temperature superconductivity can emerge in a system with only Fermi pockets and coexist with strong antiferromagnetic order, offering new insights into the pairing mechanism in high temperature cuprate superconductors.