I'd like to make a texture pack surely.

My tip is too take things easy :D
Do not use heavy colors unfitting to other colors in the same skin, try to make them look good with each other, google color palettes or if that is not helping jsut try to make all colors look bright and colorful or make all colors a but dull and almost of one color ;D
As for hands, noses and little textures, You do not necesseraly need to put details into those, Look at what kind of shoes I make, usually only of one color jsut shaded, rarely has detail, noses are either left out or made bright on one side and darker on the other.
As for muscles just google a pic of a body anatomy (nekkid jajaja) of the gender you are working with and study where their body is dark because it is not getting that much light and make the skin darker there as well, do the same when you are making the bright parts.
To experience with different colors but not necesseraly gradients try using Danori's style, a great skinner, recently is taking a long break from skinning sadly but his style is oustanding in blocky shading and of course there are many guides for getting nice colors! :D Try this!
Make a palette of the colors you will be using before skinning and use those. Later you can expand a palette with more colors and such and have detailed colors and textures everywhere!
Two thing to look out:
Always use the correct, best looking color everywhere
and always have them shaded (for example you leave the body parts of your skins unshaded while clothes and hair and such are shaded.)
And things might be one long message already but girls do not have that big muscles jsut use dark on the inside of the arms, bright colors on the outside, make the top of the shoudlers bright and you are basically good to go, for boy skins jsut add shading under the shoulder and bicep and where muscles are.

Good luck!