Add alpha cutout and lighting to custom unlit shader

Hello, I'm currently using a shader to render PS1-style graphics (affine mapping and fixed point vertices), but it is an unlit shader, and I would really like to have per-vertex lighting and alpha cutout for the textures, but I have no idea on how to achieve that.

 Shader "PSX"
 {
     Properties
     {
         _MainTex("Texture", 2D) = "white" {}
         //_Color("Color", Color) = (0.5, 0.5, 0.5, 1)
         _GeoRes("Resolution", Float) = 40
     }
     SubShader
     {
         Pass
         {
             CGPROGRAM
             #include "UnityCG.cginc"
             #pragma vertex vert
             #pragma fragment frag
 
             struct v2f
             {
                 float4 position : SV_POSITION;
                 float3 texcoord : TEXCOORD;
             };
 
             sampler2D _MainTex;
             float4 _MainTex_ST;
             //float4 _Color;
             float _GeoRes;
 
             v2f vert(appdata_base v)
             {
                 v2f o;
 
                 float4 wp = mul(UNITY_MATRIX_MV, v.vertex);
                 wp.xyz = floor(wp.xyz * _GeoRes) / _GeoRes;
 
                 float4 sp = mul(UNITY_MATRIX_P, wp);
                 o.position = sp;
 
                 float2 uv = TRANSFORM_TEX(v.texcoord, _MainTex);
                 o.texcoord = float3(uv * sp.w, sp.w);
 
                 return o;
             }
 
             fixed4 frag(v2f i) : SV_Target
             {
                 float2 uv = i.texcoord.xy / i.texcoord.z;
                 return tex2D(_MainTex, uv);
             }
 
             ENDCG
         }
     }
 }