i have experience in retopology blender files for almost 7 years now, mostly for my own projects and because i started with very low processing power so i learned some tricks, i can analyse and retopo most of your blender files, then i can make some normals and other tricks i learned to make it look better with less tris and decent textures, for normals, light paths and other stuff that you like/need, riggin the mesh is no problem for me, but i would need to know if you want keybones or the base structure
and depending of the model i can reduce from 975122 to 9100 tris as an example. (the example is from a model i made some time ago)