For the first 2 things, you can fix them by yourself easily. Go to the material area for example cappy or skin texture, look for the textures that has been used, check on their resolution. Is it 4K? Enable compression, tune it down to 2K or even better 1K, normal quality compression, 50%, apply. Do that to every texture.

Shaders can be tricky. Too many decals, effects, unnecessary cubemap shadings and so on can drag down the optimization quite well. Disable unnecessary effects and texture assignments.

About UV stuff, that requires blender skills, and since you are asking for optimization, that means you probably don't have the skillset to do that on your own - I would take over that part, if you are willing to pay for the service. Depending on the amount of clothing sets - one single set with all the logics would start at 10€, any additional set +5€.

If you want everything in a full complete package rework (textures, materials, shaders, physbones, colliders), we can talk about that price, just hit me up.