Quantum computers based on rare-earth-ion-doped crystals show promising properties in terms of scalability and connectivity if single ions can be used as qubits. Through simulations, we investigate gate operations on such qubits and discuss how gate and system parameters affect gate errors, the required frequency bandwidth per qubit, and the risk of instantaneous spectral diffusion (ISD) occurring. Furthermore, we examine how uncertainties in the system parameters affect the gate errors, and how precisely the system needs to be known. We find gate errors for arbitrary single-qubit gates of $2.1\cdot 10^{-4}$ when ISD is not considered and $3.4\cdot 10^{-4}$ when we take heed to minimize it. Additionally, we construct two-qubit gates with errors ranging from $5\cdot 10^{-4} \rightarrow 3\cdot 10^{-3}$ over a broad range of dipole-dipole interaction strengths.