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The room-temperature van der Waals itinerant ferromagnet Fe5GeTe2 (TC=270K) has become an increasingly attractive material for spintronic and valleytronic applications, owing to recent work [1,2] detailing its magnetic and structural properties doping on the Fe sites. The influence of intra-layer exchange, interlayer exchange, stacking faults, and intra-layer registry on the compound’s magnetic phase transitions is not yet rigorously understood. Here we perform ab-initio density functional theory calculations of the structural, electronic, and magnetic properties of pristine and doped Fe5GeTe2. In particular, we compute symmetric and antisymmetric Heisenberg exchange Hamiltonian coupling parameters in the pristine and doped cases, and identify magnetic phases, assess their stability and dynamics, and compare with experiments.