texel density and texture mapping optimization

So, although this is not very much a masterpiece product in texture painting… i can’t help
but i think these textures are very fine for model of this size.

Is there a way to decide texel density and how many maps will a character of N numbers of polygon take, while
also ensuring the texture are not stretched, “diagonally” stretched, blurry, while also maximizing the texture map placement?

The key summary:
texel density per unfold polygons, texel density per maps,
how many maps for a character, optimal unfold polygon placement, rotations and size?

Here’s a particular target i’m looking to achieve.