The advent of large-scale renewable energy and High voltage direct current (HVDC) transmission has resulted in stability problems in frequency and voltage. Grid-forming (GFM) strategies are characterized by excellent voltage and frequency support properties. Nevertheless, it is not feasible to precisely delineate the precise mathematical relations between GFM converter capacity and the associated stability margin. This paper addresses the optimal configuration of GFM converters in a large receiving-end power grid scenario with a significant proportion of renewable energy and HVDC feed-in. It presents a GFM converter evaluation method constrained by static voltage and frequency security. Firstly, the GFM converter technology based on virtual synchronous machine control is introduced, with a detailed explanation of its control frame. Secondly, the principles of how GFM control improves the static stability limit and frequency dynamic response characteristics are analyzed in depth, and a comprehensive assessment of GFM converter requirements is conducted by combining static stability margin constraints and frequency security constraints. Finally, the effectiveness of the proposed method is verified through a modified IEEE 39-bus model based on the Matlab/Simulink platform.